AMC 8 1986 Problem 12

The table below displays the grade distribution of the $30$ students in a mathematics class on the last two tests. For example, exactly one student received a 'D' on Test 1 and a 'C' on Test 2 (see circled entry). What percent of the students received the same grade on both tests?

$\text{(A)}\ 12\% \text{(B)}\ 25\% \text{(C)}\ 33\frac{1}{3}\% \text{(D)}\ 40\% \text{(E)}\ 50\%$