An example of direct variation is:

C. y = 5x

In a direct variation, $y$ varies directly with $x$, which means that if $x$ increases, $y$ increases in proportion. This relationship can be expressed as $y = kx$, where $k$ is a constant (in this case, $k = 5$).

Would you like more details on direct variation or any related concepts? Here are some questions to consider:

1. What is the general formula for direct variation?
2. How can you identify direct variation from a set of points?
3. Can direct variation be represented in different forms?
4. What are some real-world examples of direct variation?
5. How does direct variation differ from inverse variation?

Tip: Remember that in direct variation, the ratio of $y$ to $x$ remains constant.