1. Given real numbers $a, b$ satisfy $\frac{1}{a}+\frac{1}{b}=1, M=$ $\frac{b}{a}+\frac{a}{b}, N=\frac{b}{a^{2}}+\frac{a}{b^{2}}$. Then the relationship between $M$ and $N$ is ( ).
(A) $M>N$
(B) $M=N$
(C) $M<N$
(D) Uncertain