什么情况下应进行新增危害因素识别？
参考答案：开工作业前、录井作业过程中。
要提高电力系统的可靠性，应从哪些方面入手？
He didn’t to return earlier than 3 o’clock.()
A. was not expected
B. did not expect
C. was expected not
D. was not expecting
