The possibility____ pleasant smells might reduce pain has recently been suggested by new research.
| A．which | B．why | C．that | D．whether |
In the library, I found a useful book ______ how to use English grammar.
| A．to explain | B．explained | C．having explained | D．explaining |
Many websites have been _______ to help people study foreign languages.
| A．set off | B．set up | C．set down | D．set out |
—What do you think of Sam, the newcomer? —Well, he talks as if he ________ everything.
| A．had known | B．has known | C．knew | D．will know |
A great number of visitors __________ attracted to my hometown, and the number of foreigners there _______ quite large.
| A．are; are | B．are; is | C．is; are | D．is; is |
Kathy told me that all the doors and windows _______ when she arrived this morning.
| A．have cleaned | B．have been cleaned |
C．had cleaned | D．had been cleaned |