2. Given complex numbers $z_{1}$ and $z_{2}$, and
$$
\left|z_{1}\right|=2\left|z_{2}\right|=2,\left|z_{1}+z_{2}\right|=\sqrt{7} \text {. }
$$

Then $\left|z_{1}-z_{2}\right|=(\quad)$.
(A) $\sqrt{5}$
(B) $\sqrt{7}$
(C) 3
(D) $\sqrt{3}$
2. D.

It is known that,
$$
\left|z_{1}-z_{2}\right|=\sqrt{2\left|z_{1}\right|^{2}+2\left|z_{2}\right|^{2}-\left|z_{1}+z_{1}\right|^{2}}=\sqrt{3} \text {. }
$$