Answer:
A. Radii of congruent circles are equal.
Explanation:
We have been given an incomplete sentence. We are supposed to fill in the blank from our given choices.
Sentence:
Radii of ______ circles are equal.
We know that radius of a circle is distance from the center circle to any point on the circle.
The radii of two circles will be equal, if and only if, both circles are congruent, therefore, the correct choice is opton A.