Which of the following strategies will show that the equation 2×3y=12 is not a function of a x?

A. Fill in a value for x and solve for y
B. Fill in a value of y and solve for x
C. Find a set of value for x and y such that 2x + 3y does not equal to 12
D. There is no strategy that can be used because 2x + 3y is a function of x