高处作业的高度在（）时，称为一级高处作业。
A．2米以上
B．2米至5米
C．2米至7米
D．7米以上
参考答案：B
______ the worker’s working efficiency, the manager will allow him to have a coffee break.
A．Improving
B．To improve
C．Having improved
D．Improved
配合分为几种？
