1. Calculate the value of $(\sqrt{30}+\sqrt{21}-3)(\sqrt{3}+\sqrt{10}-\sqrt{7})$ equals ( ).
(A) $6 \sqrt{7}$
(B) $-6 \sqrt{7}$
(C) $20 \sqrt{3}+6 \sqrt{7}$
(D) $20 \sqrt{3}-6 \sqrt{7}$
$\begin{array}{l}\text { I. A. } \\ \text { Original expression }=\sqrt{3}(\sqrt{10}+\sqrt{7}-\sqrt{3})(\sqrt{3}+\sqrt{10}-\sqrt{7}) \\ =\sqrt{3}[\sqrt{10}+(\sqrt{7}-\sqrt{3})][\sqrt{10}-(\sqrt{7}-\sqrt{3})] \\ =\sqrt{3}\left[(\sqrt{10})^{2}-(\sqrt{7}-\sqrt{3})^{2}\right] \\ =\sqrt{3}(10-7+2 \sqrt{21}-3)=6 \sqrt{7} .\end{array}$