Chọn khẳng định đúng? (căn bậc hai của 14-căn bậc hai của 7/1-căn

A. $\left(\frac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}+\frac{\sqrt{15}-\sqrt{5}}{1-\sqrt{3}}\right)$$:\frac{1}{\mathrm{a}\left(\sqrt{7}-\sqrt{5}\right)}=2\mathrm{a}$

B. $\left(\frac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}+\frac{\sqrt{15}-\sqrt{5}}{1-\sqrt{3}}\right)$$:\frac{1}{\mathrm{a}\left(\sqrt{7}-\sqrt{5}\right)}=\frac{2}{\mathrm{a}}$

C. $\left(\frac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}+\frac{\sqrt{15}-\sqrt{5}}{1-\sqrt{3}}\right)$$:\frac{1}{\mathrm{a}\left(\sqrt{7}-\sqrt{5}\right)}=-2\mathrm{a}$

D. $\left(\frac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}+\frac{\sqrt{15}-\sqrt{5}}{1-\sqrt{3}}\right)$$:\frac{1}{\mathrm{a}\left(\sqrt{7}-\sqrt{5}\right)}=\frac{-\mathrm{a}}{2}$