Which CSS property is used to add space around an element's content?

The correct choice is C, padding, because this CSS property specifically adds space between an element's content and its border. When you apply padding to an element, it creates an inner space that pushes the content away from the edges of the container. This adjustment effectively enhances the layout and readability of the content within the element, allowing for a cleaner presentation.

Padding can be set in specific values for each side of the element (top, right, bottom, left) or can be applied uniformly. This flexibility is particularly useful when designing responsive layouts or ensuring visual consistency across various elements on a webpage.

While other properties like border, margin, and width also influence layout, they each serve different functions — borders create a line around an element, margins define the outer space between elements, and width specifies the size of the element itself. Padding is distinct in its role of modifying the space directly around the content inside the element.