The correct option is
A Explanation for the correct option.
Step 1. Find the value of at .
It is given that , now substitute .
Step 2. Differentiate with respect to .
In the equation take log on both sides and simplify.
Now differentiate both sides with respect to .
Step 3. Find the value of at .
Now in the equation substitute and to find the value of at .
Hence, the correct option is A.