1. Given $m>1, a=\sqrt{m+1}-\sqrt{m}, b=$ $\sqrt{m}-\sqrt{m-1}$. Then, ( ).
(A) $a>b$
(B) $a<b$
(C) $a=b$
(D) The size of $a$ and $b$ depends on the value of $m$
-.1.B.
Since $a=\frac{1}{\sqrt{m+1}+\sqrt{m}}, b=\frac{1}{\sqrt{m}+\sqrt{m-1}}$, and $\sqrt{m+1}>\sqrt{m}>\sqrt{m-1}>0$, then $a<b$.