1973 AHSME Problem 16

If the sum of all the angles except one of a convex polygon is 2190^{\circ}, then the number of sides of the polygon must be

\textbf{(A)}\ 13 \qquad \textbf{(B)}\ 15 \qquad \textbf{(C)}\ 17 \qquad \textbf{(D)}\ 19 \qquad \textbf{(E)}\ 21

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