1. If real numbers $a, b$ satisfy $a^{2}+b^{2}=4$, then
$$
\sqrt{a(b-2)}+\sqrt{a b-3 a+2 b-6}
$$

the value is ( ).
(A) 0
(B) $\sqrt{2}$
(C) 2
(D) 4
1. C

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