question_answer

If \[f(x)=\log \left( \frac{1+x}{1-x} \right)\], then \[f\left( \frac{2x}{1+{{x}^{2}}} \right)\]is equal to

A)  \[2f(x)\]                               

B)  \[f(2x)\]

C)  \[2f(-x)\]              

D)         \[f(x)\]