The correct answer is C. border-style.
The border-style property is a shorthand property for the border-top-style, border-right-style, border-bottom-style, and border-left-style properties. It takes a single value that specifies the style for all four borders of an element.
The possible values for the border-style property are:
- none: No border.
- solid: A solid border.
- dashed: A dashed border.
- dotted: A dotted border.
- double: A double border.
- groove: A groove border.
- ridge: A ridge border.
- inset: An inset border.
- outset: An outset border.
For example, the following CSS code will create a solid black border for all four sides of an element:
border-style: solid black;
The border-top-style, border-right-style, border-bottom-style, and border-left-style properties are all longhand properties that specify the style for the top, right, bottom, and left borders of an element, respectively. They take the same values as the border-style property.
For example, the following CSS code will create a solid black border for the top and bottom borders of an element, and a dashed border for the left and right borders:
border-top-style: solid black;
border-bottom-style: solid black;
border-left-style: dashed;
border-right-style: dashed;
The border-up property is not a valid CSS property.