参与肩外展运动的主要肌肉是：（）.
A.背阔肌和大圆肌
B.三角肌和冈上肌
C.胸大肌
D.冈上肌
E.大小菱形肌
参考答案：B
The girl often helps her mother _____ the housework. [ ]
A. do
B. does
C. doing did
D. did
液体在其蒸气压与外压相等时就开始沸腾。
