$$\frac{1}{\sqrt{12 - 2\sqrt{35}}} - \frac{2}{\sqrt{10 + 2\sqrt{21}}} = $$

A

$$\frac{1}{\sqrt{8 - 2\sqrt{15}}}$$

B

$$\frac{1}{\sqrt{8 + 2\sqrt{15}}}$$

C

$$\frac{1}{\sqrt{7 - 2\sqrt{15}}}$$

D

$$\frac{1}{\sqrt{7 + 2\sqrt{15}}}$$