1. The modern mocroscope is no longer the mocroscope ____it was before.C
A which B whose C that D what
请问为什么不可以选则A?
2. One light year is the distance ___light travels in one year.A
A in which B that C as D what
我除了知道不选择D 其他我认为都可以啊
3.Mr Smith will move into his new house next Mondey , ___it will be completely finished.
A by that time B by which time C by then D by the time
这道题正确答案我都不知道 请详细讲解一下每个选项
4.I am pleased with what you have given me and ___you have told me.B
A that B all that C which D all what
这道题为什么不可以选择 A 我知道ALL 必须和THAT 但是如果不用ALL 不可以吗？
5.More niddle_aged persons suffer from heart trobule___is generally believed.C
A which B that C as D than
ABC 不是都可以做主语吗 为什么要选择C?

第一题还有一种表达的形式就是：The modern mocroscope is no longer what it was before.
这里的的 what 必须要用 the mocroscope that 来代替才行!记住了，what = something/anything/all that。
第三题选B，这是一个非限制性定语从句。
第四题所填部分要和前面的对应，因此是what，而what = allthat，千万不能没all，没它的话就构不成从句了，从句中就缺了主语了。
建议你多看点关于定语从句这方面的语法。