5、E-mail, as well as telephone, ______ an important part in daily communication.

A．is playing

B．have played

C．are playing

D．Hoped

防止重大工业事故发生的第一步是（）。

A.辨识或确认高危险性的工业设施（危险源）

B.制订出危险物质标准

C.制订出临界量标准

D.确定可能发生事故的潜在危险源