1.___ is known to all, too much smoking will cause lung cancer.

A. That B. It C. As D. What

【答案】C 固定用法as is known to all：众所周知。本句的意思是：“众所周知，吸烟过多会引起肺癌。B 用于it is known to all that…句型。

2.The investigation, ___ will soon be published, was made by John.

A. at which the results B. the results on which

C. whose results D. at whose results

【答案】C 此句考查非限制性定语从句。C选项正确,whose在从句中作定语;whose results=the results of which =the results of the investigation,定语从句修饰investigation;B选项中的on改成of就对了。

3. ______ is well-known, the environment in China is badly in need of improvement.

A. It B. That C. As D. What

【答案】C此题考查的是as 引导的特殊定语从句。As is well known/ as is known to all/ as we all know：众所周知。

4. They overcame all the difficulties and fulfilled the plan ten days ahead of schedule, ____ was something we had not expected.

A. that B. this C. it D. which

【答案】D 逗号后为非限制性定语从句，只能由which 或者who 引导，不能用 that。

5. ____ is well known, light, like heat, is a form of energy.

A. It B. What C. Just as D. As

【答案】D句意为：“如我们所知，光跟热能一样是一种能量的形式。”as is well known 为非限定性定语从句，修饰整个主句，意为“如我们所知”;as 代表整个主句“光跟热能一样是一种能量的形式。”