Answer:
C is the correct answer.
Step-by-step explanation:
Look at the X values for each coordinate pair. If an X value is represented twice with different Y values, it is not a function. If no X value is repeated, or it is repeated but has the same Y value, then it is a function. A has two values for x = 1, B has two values for x = -3, D has two values for x = 7, but C does not, so it is the correct answer.