人体生命活动的原动力是指（）
A.先天之精气
B.后天之谷气
C.宗气
D.元气
E.卫气
参考答案：D
在双代号时标网络计划中，某工作箭线上没有波形线，则该工作( )。
A．为关键工作
B．总时差为0
C．自由时差为0
D．总时差：自由时差
Jenny went into the room, took off her coat and _____ down on a sofa.[ ]
A. would sit
B. was sitting
C. sat
D. had sat
