A2. What is the value of the product $x \cdot y$, if $3^{x}=a$ and $a^{y}=81$?
(A) 4
(B) 3
(C) 12
(D) 0
(E) 1
A2. Since $81=a^{y}=\left(3^{x}\right)^{y}=3^{x y}$, it follows that $x y=4$. Therefore, the correct answer is $A$.