Only when we saw the photos about the air crash ______ how terrible it was.
| A．we knew | B．we had known | C．did we know | D．had we known |
While playing ping-pong, our eyes see the ball coming, judge its speed and then hit it back ________ it should go.
| A．when | B．why | C．what | D．where |
I was about to leave my house________the phone rang.
| A．while | B．when | C．as | D．after |
.________they were singing, the teacher came in.
| A．Before | B．after | C．As | D．Until |
All that can be eaten _______ eaten up.
| A．are being | B．has been | C．had been | D．have been |
I can never forget the day _______ we worked together and the day ______ we spent together.
| A．when; which | B．which; when | C．what; that | D．on which; when |