题目

如图，已知直角三角形的两条直角边分别为a、b，以a为直径画一个半圆．若甲、乙两阴影部分的面积相等，则用a的代数式表示b= ． 答案： —Has the little boy passed ______ P.E. test? —He has tried twice, and the teacher will allow him to have _____ third try.          A. the; 不填    B. a; the   C. the; a   D. the; the