优等劳动力市场的特征有（）。
A．劳动力市场的就业条件好
B．工资福利水平较低
C．工作环境良好
D．职业保障性强
参考答案：A, C, D
— Can you go swimming with us this afternoon?
— Sorry, I can't. I ______ take care of my little sister at home because my mother is ill. [ ]
A. can
B. may
C. must
D. would
水泥粉煤灰碎石桩施工垂直度允许偏差为（）。
A.1%
B.2%
C.5%
