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：眾所周知。本句的意思是：“眾所周知，吸煙過多會(huì)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語從句。C選項(xiàng)正確,whose在從句中作定語;whose results=the results of which =the results of the investigation,定語從句修飾investigation;B選項(xiàng)中的on改成of就對了。
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此題考查的是as 引導(dǎo)的特殊定語從句。As is well known/ as is known to all/ as we all know：眾所周知。
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 逗號后為非限制性定語從句，只能由which 或者who 引導(dǎo)，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句意為：“如我們所知，光跟熱能一樣是一種能量的形式。”as is well known 為非限定性定語從句，修飾整個(gè)主句，意為“如我們所知”;as 代表整個(gè)主句“光跟熱能一樣是一種能量的形式。”
6. The day breaks ________the birds are singing.
A. in that B. which C. on that D. in which
