2. Let $a=\sqrt{2}-1, b=\sqrt{5}-2, c=\sqrt{10}-3$. Then the size relationship of $a$, $b$, and $c$ is ( ).
(A) $a<b<c$
(B) $a<c<b$
(C) $b<c<a$
(D) $c<b<a$
2. D.

From the given, we know that $a-b=\sqrt{2}+1-\sqrt{5}$.
And $(\sqrt{2}+1)^{2}-5=2 \sqrt{2}-2>0$, thus, $a>b$.
Similarly, $b>c$.