The correct answer is: D. Both (C) and (D)

A rule consists of a selector and a declaration.

A selector is a pattern that matches elements in the document. It can be a simple tag name, a class name, or an ID.

A declaration is a statement that specifies how an element should be displayed. It has a property name and a value.

For example, the following rule matches all elements with the class “red”:

.red {
color: red;
}

This rule specifies that all elements with the class “red” should have a red color.

Here is another example:

“`

header {

background-color: blue;
}
“`

This rule specifies that the element with the ID “header” should have a blue background color.

I hope this helps! Let me know if you have any other questions.