1. If for all real numbers $x, x^{2}-2 \sqrt{a} x+b$ is always positive, and
$$
\begin{array}{c}
M=2 \sqrt{b^{2}+2 b+1}-\sqrt{(a+b+2)^{2}}- \\
\sqrt{(a-b-3)^{2}},
\end{array}
$$

then the value of $M$ is ( ).
(A) 3
(B) -3
(C) $-2 a+2 b-3$
(D) $4 b+7$
- 1. B.

From the problem, we know
$$
\Delta=(-2 \sqrt{a})^{2}-4 \times 1 \times ba \text {. }
$$

Since $\sqrt{a}$ is defined, therefore, $a \geqslant 0$.
Thus, $M=2|b+1|-|a+b+2|-|a-b-3|$
$$
=2(b+1)-(a+b+2)+(a-b-3)=-3 .
$$