You already have the correct answer, but to expand on it a bit: In HTML there are elements that generally have a start and an end tag, which are called normal elements, and elements that only have a start tag, which are called void elements.
- Examples of normal elements: <p>…</p> and <a>…</a>.
- Examples of void elements: <img> and <br>.
The <audio> element is a normal element, so it should have a start and an end tag—e.g. <audio>…</audio>.