AHSME 1950 Problem 7

If the digit $1$ is placed after a two digit number whose tens' digit is $t$, and units' digit is $u$, the new number is: $\textbf{(A)}\ 10t+u+1 \textbf{(B)}\ 100t+10u+1 \textbf{(C)}\ 1000t+10u+1 \textbf{(D)}\ t+u+1 \\ \textbf{(E)}\ \text{None of these answers}$