AHSME 1996 Problem 16

A fair standard six-sided dice is tossed three times. Given that the sum of the first two tosses equal the third, what is the probability that at least one "2" is tossed? $\text{(A)}\ \frac{1}{6} \text{(B)}\ \frac{91}{216} \text{(C)}\ \frac{1}{2} \text{(D)}\ \frac{8}{15} \text{(E)}\ \frac{7}{12}$