1959 AHSME Problem 7

The sides of a right triangle are a, a+d, and a+2d, with a and d both positive. The ratio of a to d is: \textbf{(A)}\ 1:3 \qquad\textbf{(B)}\ 1:4 \qquad\textbf{(C)}\ 2:1\qquad\textbf{(D)}\ 3:1\qquad\textbf{(E)}\ 3:4

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