图复制不上来，就是一个三角形内接于一个圆的图
In the figure shown, triangle ABC is inscribed in the circle. What
is the circumference of the circle?
(1) AB is a diameter of the circle.
(2) The ratio of the lengths of BC, AC, and AB, respectively,
is 3 : 4 : 5.
答案是A，可是也没有告诉三角形的具体任何数值，也没有半径阿？ | 
