We can’t figure out ______ quite a number of insects and birds are dying out．
| A．that | B．as | C．why | D．when |
Mother wanted to be a good provider, a role she ______ since her marriage to Father.
| A．shoulders | B．shouldered |
| C．is shouldering | D．has been shouldering |
It will make ______big difference if this experiment becomes ______ success.
| A．a; a | B．a; the | C．/; / | D．a; / |
By the time my mother came back from work, my sister and I ________ supper and were waiting for her at the table.
| A．have cooked | B．were cooking | C．had cooked | D．would cook |
As is reported, it is 100 years______Qinghua University was founded.
| A．when | B．before | C．after | D．since |
He had his camera ready____ he saw something that would make a good picture.
| A．even if | B．if only | C．in case | D．so that |