A professor and writer ____ present at the meeting last night.
| A．had been | B．were | C．is | D．was |
So many uses have been discovered for this wood ____ the supply of white pine is becoming smaller and smaller.
| A．then | B．what | C．that | D．which |
The truth, Sir, is that the old man____ across the street when my car hit him.
| A．was to walk | B．had been walking | C．walked | D．was walking |
I wrote to my parents once a week,____ I was too busy with my teaching work.
| A．it | B．unless | C．when | D．as |
However, at times this balance in nature is disturbed, ____ a number of possibly unforeseen effects.
| A．lying in | B．calling in | C．taking in | D．resulting in |
--- He has to finish the experiment today. He must be in the lab,____?
---That s quite possible.
| A．mustn't he | B．won't he | C．doesn't he | D．isn't he |