The Correct answer is C.

Explanation

Choice (C) is correct. Sinceis equilateral, each of its angles has measure?. It follows that?has measure?. Since?and?are radii of the same circle, they are of equal length, and sois isosceles. Hence?and?each have measure?. Thus?has measure?, and so?is a?right triangle. Since?, the side opposite the?? angle in?, is of length?, it follows that?, the side opposite the?angle, is of length?.