The correct answer is C
Explanation
The volume of a cylinder with radius r and height h is equal to pi times (r^2) times h. Therefore, pi times (r^2) times (6) = 54 times pi and r^2 = 9, so the radius of the cylinder is 3. The circumference of a circle with radius r is equal to 2 times pi times r; therefore, the circumference of the base is equal to 6 times pi.