a. ratio of the diameter to the radius the ratio of the diameter to the radius for any circle is always going to be 2:1 because the diameter is 2 times the legnth of the radius any time so A is not the right answer
b. the degrees of the circle is always 360, the circumference is the distance around the circle, so that would be a good indicator since 360 is constant, but the circumference can change, and if they are the same, then the circles are similar. so B is the right answer
c. Ratio of area to circumference. area=pir^2, and circumference=2pir this is a good indicator becuase the ratio of the area and the circumference is different for every circle so c is the right answer
D. the ratio of the diameter to the circumference diameter=2r circumference=2pir circumference=pi time diameter so the ratio of the diameter is 1:pi this is not a good indicator so this is not the right answer
The answers are B and D, but if the teacher asks for only one, then I would pick c
