(A) File formats like MP3, MP4, and WebM are called container formats.

• Correct.
  MP3, MP4, and WebM are indeed container formats. A container format holds various types of media (such as audio, video, and metadata) together in a single file. For example:
  • MP3 is an audio container.
  • MP4 is a multimedia container, typically holding both video and audio.
  • WebM is also a multimedia container format used for web video.

(B) Heading level 1 has an implicit style.

• Correct.
  In HTML, heading elements like <h1> have implicit styles, which are usually defined by the browser's default stylesheet. By default, <h1> elements are often bold and have a larger font size compared to other text elements.

(C) Elements have no content and are called void elements.

• Correct.
  Void elements (also called self-closing elements) are HTML elements that do not have any content or closing tags. Examples include <img>, <br>, <input>, <hr>, etc. They do not contain any nested content and are written with a single opening tag.

(D) All of these.

• Since all three individual statements (A), (B), and (C) are correct, the correct answer is: (D) All of these.