肺通气的直接动力来自于()
A.胸内压与大气压之差
B.胸内压与肺内压之差
C.肺内压与大气压之差
D.气体的分压差
E.呼吸肌收缩和舒张
参考答案:C
The reason why they failed the test was ____ they didn’t sleep at all the night before.
A.because
B.why
C.that
D.for which
请从所给的四个选项中,选择合适的选项,使之呈现一定的规律性。( ) [*]