AHSME 1973 Problem 31

In the following equation, each of the letters represents uniquely a different digit in base ten: $$(YE) \cdot (ME) = TTT$$ The sum $E+M+T+Y$ equals $\textbf{(A)}\ 19 \textbf{(B)}\ 20 \textbf{(C)}\ 21 \textbf{(D)}\ 22 \textbf{(E)}\ 24$