By the time Billy was 6, he in the sea.
| A．had already swum | B．was already swimming |
| C．has already swum | D．already swam |
Does ________ matter much if they do not come tomorrow?
| A．this | B．it | C．that | D．he |
The bell ____ the end of the period rang and we had to stop our discussion
| A．indicating | B．indicated |
| C．to be indicated | D．being indicated |
One-third of the area ________ covered with trees. About seventy percent of the trees _______ been planted recently.
| A．is; has | B．is; have | C．are; have | D．are; has |
Neither Tom nor his parents ________ at home.
| A．is | B．are | C．has | D．was |
--It really shocked us that he should have made such_______ rapid progress in his study in such a short time!
--No surprising. He has been making _______ most of his spare time to study.
| A．a; the | B．a; / | C．/; the | D．/; / |