Will give Brainliest and 50 points!

C is a function. The must pass the vertical (up and down) line test. Put a vertical line on it. It it touches 2 points it is not a function.
A B and D are not functions because when you draw a vertical line (Vertical line test) the line passes through 2 points of the graph where as in C, it is a function because when you draw a vertical line through the graph, the line only hits 1 point