```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">

<title>Listening Discrimination – /θ/ and /d/</title>
<meta name="description" content="Listening discrimination practice contrasting /θ/ and /d/ in British English.">
<meta name="keywords" content="British English, pronunciation, phonology, phonemes, listening discrimination, minimal pairs, language learning, EFL, ESL, ELT">

<style>
@page {
    size: A4;
    margin: 20mm;
}

* {
    box-sizing: border-box;
}

html, body {
    margin: 0;
    padding: 0;
}

body {
    background: #e5e5e5;
    color: #222;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 17px;
    line-height: 1.6;
}

.page {
    width: 210mm;
    min-height: 297mm;
    margin: 15mm auto;
    padding: 20mm 25mm;
    background: white;
    box-shadow: 0 0 10px rgba(0,0,0,.22);
}

.screen-nav {
    margin: 0 0 20px;
    padding: 8px 0;
    text-align: center;
    font-size: 14px;
    border-bottom: 1px solid #ddd;
}

.screen-nav a {
    color: #245a8d;
    text-decoration: none;
    margin: 0 6px;
}

.screen-nav a:hover,
.screen-nav a:focus {
    text-decoration: underline;
}

h1 {
    margin: 0 0 18px;
    text-align: center;
    font-size: 21px;
    line-height: 1.3;
    font-weight: 600;
}

.introduction {
    margin: 0 auto 24px;
    text-align: center;
}

.phoneme {
    font-family: "Lucida Sans Unicode", "Arial Unicode MS", Arial, sans-serif;
}

.instructions {
    max-width: 650px;
    margin: 0 auto 28px;
    text-align: center;
}

.exercise {
    max-width: 620px;
    margin: 0 auto;
    text-align: center;
}

.question-number {
    margin-bottom: 18px;
    font-size: 18px;
    font-weight: bold;
}

.listen-area {
    margin: 20px 0 28px;
}

.listen-button {
    padding: 10px 24px;
    border: 1px solid #999;
    border-radius: 4px;
    background: #f3f3f3;
    color: #222;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 17px;
    cursor: pointer;
}

.listen-button:hover,
.listen-button:focus {
    background: #e6e6e6;
}

.question {
    margin-bottom: 18px;
    font-size: 18px;
}

.answers {
    display: flex;
    justify-content: center;
    gap: 30px;
    margin: 20px auto;
}

.answer-button {
    width: 180px;
    min-height: 52px;
    padding: 10px 15px;
    border: 1px solid #999;
    border-radius: 4px;
    background: white;
    color: #222;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 18px;
    cursor: pointer;
}

.answer-button:hover,
.answer-button:focus {
    background: #f1f1f1;
}

.answer-button.correct {
    background: #e4f2e4;
    border-color: #4d8b4d;
}

.answer-button.incorrect {
    background: #f7e3e3;
    border-color: #a44;
}

.feedback {
    min-height: 58px;
    margin: 20px auto;
    max-width: 560px;
    font-size: 17px;
}

.feedback strong {
    display: block;
    margin-bottom: 4px;
}

.next-button {
    display: none;
    padding: 9px 20px;
    border: 1px solid #777;
    border-radius: 4px;
    background: #eee;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 16px;
    cursor: pointer;
}

.next-button:hover,
.next-button:focus {
    background: #ddd;
}

.score {
    display: none;
    margin: 30px auto;
    padding: 18px;
    max-width: 500px;
    border-top: 1px solid #ccc;
    text-align: center;
    font-size: 18px;
}

.restart-button {
    padding: 8px 18px;
    border: 1px solid #777;
    border-radius: 4px;
    background: #eee;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 15px;
    cursor: pointer;
}

.footer {
    margin-top: 35px;
    text-align: center;
    font-size: 13px;
}
@media (max-width: 800px) {
    body {
        background: white;
    }

    .page {
        width: 94%;
        min-height: auto;
        margin: 20px auto;
        padding: 24px 28px;
        box-shadow: none;
    }

    .answers {
        gap: 15px;
    }

    .answer-button {
        width: 45%;
    }
}

@media print {
    body {
        background: white;
        font-size: 12pt;
    }

    .page {
        width: 100%;
        min-height: 0;
        margin: 0;
        padding: 0;
        box-shadow: none;
    }

    .screen-nav,
    .listen-area,
    .next-button,
    .restart-button {
        display: none !important;
    }

    h1 {
        font-size: 18pt;
    }

    .footer {
        font-size: 9pt;
    }
}

.next-exercise {
    margin: 28px auto 0;
    padding-top: 18px;
    border-top: 1px solid #ddd;
    text-align: center;
    font-size: 15px;
}

.next-exercise a {
    color: #245a8d;
    text-decoration: none;
}

.next-exercise a:hover,
.next-exercise a:focus {
    text-decoration: underline;
}

@media print {
    .next-exercise {
        display: none;
    }
}
</style>
</head>

<body>

<div class="page">

    <div class="screen-nav">
    <a href="minimal-exercises.html">Minimal Pairs: Listening exercises</a> |<a href="minimal.html">Minimal Pairs</a> |
        <a href="phono.html">L1 pronunciation problems</a> |
        <a href="index.html">Home</a>
    </div>

    <h1>
        Listening Discrimination – 
        <span class="phoneme">/θ/</span> and 
        <span class="phoneme">/d/</span>
    </h1>

    <p class="introduction">
        <span class="phoneme">/θ/</span> as in <strong>"thigh"</strong>
        &nbsp; · &nbsp;
        <span class="phoneme">/d/</span> as in <strong>"die"</strong>
    </p>

    <p class="instructions">
        Listen to the word. Then choose the word you hear.
        You can listen again if necessary.
    </p>

    <div class="exercise">

        <div class="question-number" id="questionNumber">
            Question 1 of 20
        </div>

        <div class="listen-area">
            <button type="button" class="listen-button" onclick="listen()">
                🔊 Listen
            </button>
        </div>

        <div class="question">
            Which word did you hear?
        </div>

        <div class="answers">
            <button type="button" class="answer-button"
                    id="answerA" onclick="checkAnswer(0)">
            </button>

            <button type="button" class="answer-button"
                    id="answerB" onclick="checkAnswer(1)">
            </button>
        </div>

        <div class="feedback" id="feedback"></div>

        <button type="button" class="next-button"
                id="nextButton" onclick="nextQuestion()">
            Next Question
        </button>

    </div>

    <div class="score" id="score"></div>

    <div class="footer">
        Listening discrimination practice – British English consonant contrast
    </div>
<div class="next-exercise">
    <a href="minimal2930i.html">
        Next exercise: Listening Discrimination – /θ/ and /ð/ →
    </a>
</div>

</div>

<script>

/*
    The pairs come directly from the source exercise.
    The order of the questions is randomised.
*/

const pairs = [
    ["thigh", "die"],
    ["thread", "dread"],
    ["thin", "din"],
    ["thorn", "dawn"],
    ["theme", "deem"],
    ["thug", "dug"],
    ["Perth", "purred"],
    ["worth", "word"],
    ["faith", "fade"],
    ["Keith", "keyed"],
    ["bath", "bard"],
    ["berth", "bird"],
    ["both", "bode"],
    ["death", "dead"],
    ["deathly", "deadly"],
    ["fourth", "ford"],
    ["hearth", "hard"],
    ["north", "gnawed"],
    ["author", "order"],
    ["Cathy", "caddy"]
];

let questions = [];
let currentQuestion = 0;
let score = 0;
let answered = false;

/* Shuffle an array without changing the original. */
function shuffle(array) {
    const copy = [...array];

    for (let i = copy.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        [copy[i], copy[j]] = [copy[j], copy[i]];
    }

    return copy;
}

/*
    Prepare the exercise.

    Each question contains one pair.
    The correct answer is also randomised between
    the left and right buttons.
*/
function prepareQuestions() {

    questions = shuffle(pairs).map(pair => {

        const correct = Math.floor(Math.random() * 2);

        return {
            pair: pair,
            correct: correct,
            word: pair[correct]
        };
    });
}

/* Display the current question. */
function showQuestion() {

    const q = questions[currentQuestion];

    document.getElementById("questionNumber").textContent =
        "Question " + (currentQuestion + 1) + " of " + questions.length;

    document.getElementById("answerA").textContent = q.pair[0];
    document.getElementById("answerB").textContent = q.pair[1];

    document.getElementById("answerA").className =
        "answer-button";

    document.getElementById("answerB").className =
        "answer-button";

    document.getElementById("feedback").innerHTML = "";

    document.getElementById("nextButton").style.display = "none";

    answered = false;
}

/*
    Speak the target word.

    A British English voice is requested where the
    browser provides one. If no British voice is
    available, the browser's default English voice
    is used.
*/
function listen() {

    const q = questions[currentQuestion];

    window.speechSynthesis.cancel();

    const utterance = new SpeechSynthesisUtterance(q.word);

    utterance.lang = "en-GB";
    utterance.rate = 0.75;
    utterance.pitch = 1;

    const voices = window.speechSynthesis.getVoices();

    const britishVoice = voices.find(voice =>
        voice.lang && voice.lang.toLowerCase() === "en-gb"
    );

    if (britishVoice) {
        utterance.voice = britishVoice;
    }

    window.speechSynthesis.speak(utterance);
}

/* Check the learner's answer immediately. */
function checkAnswer(choice) {

    if (answered) {
        return;
    }

    answered = true;

    const q = questions[currentQuestion];

    const buttonA = document.getElementById("answerA");
    const buttonB = document.getElementById("answerB");
    const feedback = document.getElementById("feedback");

    if (choice === q.correct) {

        score++;

        document.getElementById(
            choice === 0 ? "answerA" : "answerB"
        ).classList.add("correct");

        feedback.innerHTML =
            "<strong>Correct!</strong>" +
            "You heard <strong>" + q.word + "</strong>.";

    } else {

        document.getElementById(
            choice === 0 ? "answerA" : "answerB"
        ).classList.add("incorrect");

        document.getElementById(
            q.correct === 0 ? "answerA" : "answerB"
        ).classList.add("correct");

        feedback.innerHTML =
            "<strong>Not quite.</strong>" +
            "The word was <strong>" + q.word + "</strong>.";
    }

    if (currentQuestion < questions.length - 1) {

        document.getElementById("nextButton").style.display =
            "inline-block";

    } else {

        showFinalScore();
    }
}

/* Move to the next question. */
function nextQuestion() {

    currentQuestion++;

    showQuestion();

    window.scrollTo({
        top: 0,
        behavior: "smooth"
    });
}

/* Show the final score. */
function showFinalScore() {

    const scoreBox = document.getElementById("score");

    scoreBox.innerHTML =
        "<strong>Exercise complete</strong><br><br>" +
        "Your score: <strong>" + score +
        " out of " + questions.length + "</strong><br><br>" +
        '<button type="button" class="restart-button" onclick="restartExercise()">' +
        "Try Again" +
        "</button>";

    scoreBox.style.display = "block";
}

/* Start a completely new version of the exercise. */
function restartExercise() {

    currentQuestion = 0;
    score = 0;

    document.getElementById("score").style.display = "none";

    prepareQuestions();
    showQuestion();

    window.scrollTo({
        top: 0,
        behavior: "smooth"
    });
}

/*
    Safari and some other browsers load voices
    asynchronously. Calling getVoices() once when
    they become available helps ensure that the
    British English voice can be selected.
*/
if ("speechSynthesis" in window) {
    window.speechSynthesis.onvoiceschanged = function() {
        window.speechSynthesis.getVoices();
    };
}

/* Start the exercise. */
prepareQuestions();
showQuestion();

</script>

</body>
</html>
```