1. Given $x+\frac{1}{x}=7(0<x<1)$. Then the value of $\sqrt{x}-\frac{1}{\sqrt{x}}$ is ( ).
(A) $-\sqrt{7}$
(B) $-\sqrt{5}$
(C) $\sqrt{7}$
(D) $\sqrt{5}$
- 1. B.
$$
\text { Since }\left(\sqrt{x}-\frac{1}{\sqrt{x}}\right)^{2}=x+\frac{1}{x}-2=5(0<x<1) \text {, }
$$

Therefore, $\sqrt{x}-\frac{1}{\sqrt{x}}=-\sqrt{5}$.