题目

--How soon do you think the economy will recover?---________?A. What for       B. Who knows      C. Why not         D. How come 答案：B扇形的半径为30cm，圆心角为120°，用它做成一个圆锥的侧面，则圆锥底面半径为（ ）A．10cmB．20cmC．10πcmD．20πcm