question_answer

If \[y\sqrt{{{x}^{2}}+1}=\log \left\{ \sqrt{{{x}^{2}}+1}+x \right\},\] then \[({{x}^{2}}+1)\frac{dy}{dx}+xy+1=\]

A)  3                                

B)  2

C)  1                                

D)  0

E)  None of these