Which method is valid for proving that two circles are similar?

Question

A. Calculate the ratio of the diameter to the radius for each circle and show they are equal

B. Calculate the ratio of degrees to the circumference for each circle and show they are equal.

C. Calculate the ratio of the area to the circumference for each circle and show they are equal.

D. Calculate the ratio of the diameter to the circumference for each circle and show they are equal

Answer 1

I consider this to be a VERY POOR question. 

ALL CIRCLES ARE SIMILAR. 

This means that C / d = pi    i.e. as diameter grows, Circumference grows by a factor pi.

 

But this is NOT PROOF unless it's shown to be true for ANY two circles.