AHSME 1973 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 $\textbf{(A)}\ 13 \textbf{(B)}\ 15 \textbf{(C)}\ 17 \textbf{(D)}\ 19 \textbf{(E)}\ 21$