题目

We saw many students playing on the playground, most of them _____ girls.      A. are            B. being        C. were          D. have been 答案：B 解析: 略如图为模拟膈肌运动的示意图．则下列相关叙述中，正确的是（　　）A.甲图演示吸气，膈肌收缩B.乙图演示吸气，膈肌舒张C.甲图演示呼气，膈肌舒张D.乙图演示呼气，膈肌收缩