Question

The slope of a line is 0. What do you know about the line?

Answer 1

Your answer (C, the line is vertical) is correct

Answer 2

Your line would have to be horizontal. A vertical line yields an undefined slope.

Slope is rise over run. For a horizontal line you would have 0 rise and X amount of run or 0/x. 0 divided by anything = 0

For a vertical line, you would have the opposite, X rise and 0 run or x/0. You cannot divide by 0. It is impossible.

Therefore, your answer is the second option.