If $a$ and $b$ are positive integers, the operation $\nabla$ is defined by $a \nabla b=a^{b} \times b^{a}$. What is the value of $2 \nabla 3$ ?
(A) 36
(B) 72
(C) 3125
(D) 7776
(E) 46656
Since $a \nabla b=a^{b} \times b^{a}$, then $2 \nabla 3=2^{3} \times 3^{2}=8 \times 9=72$.

ANSWER: (B)