The telephone _____ three times in the last hour, and each time it _____ for my sister.
| A．had rung; was | B．has rung; was | C．rang; has been | D．has been ringing; is |
It is five days_____ we came here.
| A．when | B．before | C．as | D．since |
I have not seen him_____ he went to college.
| A．when | B．before | C．as | D．since |
They did not stop fighting_____ there was no enemy left.
| A．until | B．after | C．when | D．since |
I was about to leave my house _____the phone rang.
| A．while | B．when | C．as | D．after |
_____ we were singing, the teacher came in.
| A．Before | B．after | C．As | D．Until |