3. Let $n$ be a positive integer, and
$$
x=\left(1+\frac{1}{n}\right)^{n}, y=\left(1+\frac{1}{n}\right)^{n+1} \text {. }
$$

Then ( ).
(A) $x^{y}>y^{x}$
(B) $x^{y}=y^{x}$
(C) $x^{y}<y^{x}$
(D) Any of the above is possible
3. B.

Let $x=\frac{(n+1)^{n}}{n^{n}}, y=\frac{(n+1)^{n+1}}{n^{n+1}}$, taking logarithms easily yields $x^{y}=y^{x}$.