$30 \cdot 17$ is divisible by the smallest prime of $3^{11}+5^{13}$
(A) 2.
(B) 3.
(C) 5.
(D) $3^{11}+5^{13}$.
(E) None of these.
(25th American High School Mathematics Examination, 1974)
[Solution] Since $3^{11}$ and $5^{13}$ are both odd numbers, their sum must be even. Also, 2 is the smallest prime number. Therefore, the answer is $(A)$.