Example 3 Calculate the value of 
$(\sqrt{30}+\sqrt{21}-\sqrt{3})(\sqrt{3}+\sqrt{10}-\sqrt{7})$ is ( ). ${ }^{[3]}$
(A) $6 \sqrt{7}$
(B) $-6 \sqrt{7}$
(C) $20 \sqrt{3}+6 \sqrt{7}$
(D) $20 \sqrt{3}-6 \sqrt{7}$
$(2007$, National Junior High School Mathematics Competition, Tianjin Preliminary Contest)
$$
\begin{array}{l}
=\sqrt{3}[\sqrt{10}+(\sqrt{7}-\sqrt{3})][\sqrt{10}-(\sqrt{7}-\sqrt{3})] \\
=\sqrt{3}(10-7+2 \sqrt{21}-3)=6 \sqrt{7} .
\end{array}
$$

Therefore, the correct answer is (A).