The answer is B. C=πD
The answer is indeed B but let me give you the procedure so that you know why is it that:
c=2*pi*r
2r=d
so
c=pi*d
I hope this clarifies everything.
I think this was the question
If r is the radius of a circle and d is its diameter, which of the following is an equivalent formula for the circumference C=2πr?
A. C=2πd
B. C=πD
C. C=πr2
D. C=πdr
