Read the following SAT test question and then click on a button to select your answer.

In the figure above, inscribed triangle A B C is equilateral. If the radius of the circle is r, then the length of arc AXB is

(A) (2πr)/3
(B) (4πr)/3
(C) (3πr)/2
(D) (πr^2)/3
(E) (2πr^2)/3

来源:可可英语 http://www.kekenet.com/sat/201510/401637.shtml