16. He made another wonderful discovery, __________ of great importance to science.
| A．I think which is | B．which I think it is | C．which I think it | D．which I think is |
—I have learned that a large new building will be set up__________the Twin Towers once stood.
—So have I.But the American people haven’t yet got over the shock of September 11.
| A．where | B．when | C．which | D．that |
—Didn’t you buy a dress yesterday?
—No，__________I liked the colour，I didn’t like its style.
| A．since | B．if | C．when | D．though |
_________ I felt somewhat disappointed and was about to leave，something occurred which attracted my attention.
| A．Unless | B．Until | C．When | D．While |
There is no doubt that he is a good professor__________he is doing fine.
| A．but | B．because | C．so | D．yet |
__________ there are a large number of chemical factories，the air is likely to be polluted.
| A．That | B．Where | C．Once | D．As |