Tính nguyên hàm 

Câu hỏi: Tính nguyên hàm $\int \frac{dx}{\sqrt{x+1}+\sqrt{x-1}}$

A. $\frac{\left(x+1\right)\sqrt{x+1}}{3}+\frac{\left(x-1\right)\sqrt{x-1}}{3}+C$

B. $-\frac{\left(x+1\right)\sqrt{x+1}}{3}-\frac{\left(x-1\right)\sqrt{x-1}}{3}+C$

C. $\frac{\left(x+1\right)\sqrt{x+1}}{3}-\frac{\left(x-1\right)\sqrt{x-1}}{3}+C$

D. $-\frac{\left(x+1\right)\sqrt{x+1}}{3}+\frac{\left(x-1\right)\sqrt{x-1}}{3}+C$