1951 AHSME Problem 17

Indicate in which one of the following equations y is neither directly nor inversely proportional to x:

\textbf{(A)}\ x+y = 0\qquad\textbf{(B)}\ 3xy = 10\qquad\textbf{(C)}\ x = 5y \qquad\textbf{(D)}\ 3x+y = 10 \qquad\textbf{(E)}\ x/y = \sqrt{3}\qquad

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.