The answer is the option d, which is: d) 
The explanation for this problem is shown below:
1. Smplify the denominator and rewrite the numerator in this form:

2. Multiply the denominator and the numerator by the conjugated
and simplify the expression, as following:

3. As you can see, you obtain the expression shown in the option mentioned above.
Whats the diameter?
1/8(3.14) = 0.3925