All flights   because of the storm, they had to wait in the hall.

A．have put off

B．were put off

C．have been put off

D．having been put off

根据《安全生产违法行为行政处罚办法》，生产经营单位与从业人员订立协议，免除或者减轻其对从业人员因生产安全事故伤亡依法应承担的责任的，该协议______。

A．五日内生效
B．一个月内有效
C．无效
D．当即生效