The best way to prevent the air polluting _____ , but the sky is still not clear.
| A．is used | B．are used | C．has been used | D．have been used |
Owen wouldn't eat anything ________ he cooked it himself.
| A．until | B．since | C．unless | D．while |
You will be successful in the interview ________ you have confidence.
| A．before | B．once | C．until | D．though |
People who are really in need of houses will suffer heavy losses ________ the government takes measures to bring down house prices.
| A．if | B．in case | C．unless | D．since |
________ hard one may work, one cannot master a foreign language in a month or two.
| A．Whenever | B．Wherever |
| C．Whatever | D．However |
________ I really don't like art, I find his work impressive.
| A．As | B．Since | C．If | D．While |