The correct answer is: C. @media

The @media rule is a CSS at-rule that allows you to specify different styles for different media types. For example, you could use the @media rule to specify different styles for print and screen media.

The @media rule takes a media type as its argument. The media type can be any of the following:

  • all
  • audio
  • braille
  • embossed
  • handheld
  • print
  • projection
  • screen
  • speech
  • tty
  • tv

The @media rule can also take a list of media types as its argument. For example, the following rule would specify different styles for print and screen media:

```css @media all and (min-width: 600px) { / Styles for screen media / }

@media print { / Styles for print media / } ```

The @media rule can be used to specify different styles for different devices. For example, the following rule would specify different styles for mobile devices and desktop computers:

```css @media all and (max-width: 600px) { / Styles for mobile devices / }

@media all and (min-width: 600px) { / Styles for desktop computers / } ```

The @media rule can also be used to specify different styles for different output devices. For example, the following rule would specify different styles for a printer and a screen:

```css @media print { / Styles for a printer / }

@media screen { / Styles for a screen / } ```

The @media rule is a powerful tool that can be used to create responsive web designs. By using the @media rule, you can specify different styles for different devices and output devices. This allows you to create a web design that looks great on all devices.

The other options are incorrect because they are not valid CSS at-rules.