The correct answer is: A. @media
An @media rule is used to define style rules for multiple media types in a single embedded style sheet. For example, you can use an @media rule to define different styles for print and screen media.
The @charset rule is used to specify the character encoding of the document. The @font-face rule is used to define custom fonts.
Here is an example of an @media rule:
css
@media screen and (max-width: 600px) {
body {
font-size: 12px;
}
}
This rule will apply the specified style rules to all elements in the document when the document is being displayed on a screen with a maximum width of 600 pixels.