But for their common interests, they_____ cooperated so smoothly in the investigation of the case.

A．could have

B．will not have

C．could not have

D．have not

遵章守纪是指铁路职工在从事各自的职业活动中，始终按照（）的各种行为规则，一丝不苟地完成生产作业的行为。

A、商议

B、约定

C、明文规定

D、作业环节