The chairman thought _____ necessary to invite Professor Smith to speak at the meeting.
| A.that | B.it | C.this | D.him | 
We’d very much appreciate ___ if you could help us.
| A.this | 
| B.that | 
| C.it | 
| D.you | 
—Keep ___ in mind that you have to be here on time.
 —OK, I will.
| A.it | 
| B.me | 
| C.this | 
| D.one | 
The public ___ of the environmental problem will make the government take it seriously.
| A.existence | 
| B.revolution | 
| C.awareness | 
| D.evidence | 
Try on both shoes and walk around to ensure a comfortable fit ___ you know your shoe size.
| A.as if | 
| B.unless | 
| C.even if | 
| D.now that | 
I know that ___ would ever discourage him; he would never give up wanting to be a director.
| A.something | 
| B.anything | 
| C.everything | 
| D.nothing |