$$\sqrt{15 + 2\sqrt{15} + 2\sqrt{21} + 2\sqrt{35}} + \sqrt{15 - 2\sqrt{15} - 2\sqrt{21} + 2\sqrt{35}} =$$

A

$$\sqrt{5} + \sqrt{7}$$

B

$$2(\sqrt{5} + \sqrt{7})$$

C

$$2\sqrt{5}$$

D

$$2\sqrt{7}$$