For years scientists have been worried about the ______ of air pollution on the earth's natural conditions.
| A．effect | B．result |
| C．account | D．cause |
--- What did he say? ---- He said he ________ the sentence in his own words.
| A．was considering to explain | B．considered how to explaining |
| C．would consider to explain | D．was considering explaining |
I have no doubt in my mind______ they will be glad to see me.
| A．if | B．whether | C．that | D．about |
With the help of high technology, many new substances（物质）______in the past years.
| A．discovered | B．have discovered | C．had been discovered | D．have been discovered |
---- Will Joe attend the party? ----- If his wife won’t go to the party,_________.
| A．he will either | B．neither does he | C．he neither will | D．neither will he |
----- Can I go back home now? ----- You______ to leave until you ______ your work.
| A．won’t allow; finish | B．won’t be allowed; will finish |
| C．won’t be allowed; have finished | D．won’t allow; will finish |