Chọn mệnh đề đúng: nguyên hàm (1/sin^2 x + 1/cos^2x) dx = tanx -cotx + C

A. $\int \left(\frac{1}{{\sin }^{2}x}+\frac{1}{{\cos }^{2}x}\right)dx=\tan x-\cot x+C$

B. $\int \left(\frac{1}{{\sin }^{2}x}+\frac{1}{{\cos }^{2}x}\right)dx=\cot x-\tan x+C$

C. $\int \left(\frac{1}{{\sin }^{2}x}+\frac{1}{{\cos }^{2}x}\right)dx=\tan x+\cot x+C$

D. $\int \left(\frac{1}{{\sin }^{2}x}+\frac{1}{{\cos }^{2}x}\right)dx=-\cot x-\tan x+C$