The correct answer is B

Explanation

The circles each have radius 10, so AB=AD=DC=10. Since the circles are tangent at point D, segment  contains D and AC=20. 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 x=90-30=60.