The correct answer is B

Explanation

The circles each have radius 10, so?. Since the circles are tangent at point D, segment??contains D and?. Also,??and??are perpendicular because a line tangent to a circle forms a right angle with the radius at the point of tangency. Therefore,??is a right triangle with hypotenuse 20 and side??of length 10. A right triangle with one side of length one-half that of its hypotenuse is a??triangle. The??angle is opposite side?, so?.