Answer:
C
Explanation:
A proportional equation is in the form:

Where y is the dependent variable, x is the independent variable, and k is the constant of proportionality.
An important aspect of a proportional equation is that it passes through the origin. That is, it has no y-intercept (or a constant value).
From our choices, the only choices that don’t have y-intercepts are C and D.
However, D is not a linear function.
Therefore, our answer is C.
And our constant of proportionality is 1/2.