Derivative Notation Practice Test

Which of the following does NOT represent the derivative of a function $$y=f(x)$$ with respect to $$x$$?

The volume $$V$$ of a sphere, in cubic centimeters, is a function of its radius $$r$$ in centimeters, given by $$V(r) = \frac{4}{3}\pi r^3$$. What is the correct interpretation of the notation $$\frac{dV}{dr}$$?