—Do you know about the accident which happened in the center of the city?

—Yes. But it was some time           we realized the truth.

A．before

B．when

C．since

D．until

( )提高职业道德的意识，必须将学习理论和实践相结合，向革命前辈和先进人物学习，自觉地进行展示和慎独。