He opened the door to__who___where eager to seek after knowledge.答案居然是such as,不知道是我错了还是答案错了,The project is known to_____for three mouths.going on,为什么不用havebe going onJohn suggested_____anything about it until they found out more facts.答案是not say,我觉得应该后面加动名词not saying,答案是把这句话当成虚拟了,为什么?The force_____the earth attracts matter is called gravity.答案是for which,for是接在那个谓语动词后面的?This is the most important respect______civilized man can be distinguished from pri

1.楼主的题干可能有点问题；如果是填such as 这道题就是考定语从句,as为关系代词,所以应思考从句中的成分,由于eager为形容词,故从句中缺少谓语,联系be eager to do sth 渴望做某事,故题干中的where应改成were,此时填such as 便无问题.
成分分析如下：
He opened the door to_______ who 主句
___were eager to seek after knowledge定语从句（其中who为现行词,在从句中作主语）
联系关系代词的用法,故此处填such as引导定语从句.
2.The project is known to_____for three mouths.
此题考查sb/sth is known +不定式,中不定式的时态的确定问题,此处用不定式的一般时,表示其动作与"know"这一动作几乎同时发生,不强调其先后顺序；用不定式的现在进行时,表示正在进行或现阶段进行的动作；用其完成时,表示其先于“know"这一动作；所以这道题选什么,是需要语境的.由于其中有时间状语for three months,故此处用其现在完成体应该是讲得通的,或用其现在进行时,表示现阶段存在的动作,也因该是没问题的.所以,此题是可以用to be going on强调其正在进行.此题建议问一下你们老师.
The force_____the earth attracts matter is called gravity.
定语从句中的介词的确定可将先行词带入定语从句中考察,看是否需用介词以及用什么介词：故此题可转换为The earth attracts matter (for) the force.中介词的确定问题,若为短语或搭配,这需平时积累；而此处考查for的一般用法,在此处表原因.故此定语从句用for which引导.
John suggested_____anything about it until they found out more facts.此处到底是考查suggest doing sth还是考查“suggest that 主语 +（should)+动词原形”（建议~）,重点在于读懂题干意思：我们是把它理解成：
（1）用suggest doing sth那么可得
John suggested_____anything about it 主句
until they found out more facts.时间状语从句
译成汉语即为：直到他们查明更多事实真相,约翰建议对此不要做任何评论.（not 为现在分词的否定形式；until直到）
（2）用suggest that 主语 +（should)+动词原形”（建议~）其句子结构为
John suggested 主句
not say anything about it until they found out more facts.宾语从句
可译成汉语：约翰建议,直到他们查明更多事实真相前,不要对此做任何评论.（not until直到~才）
故用not say.此处重点在于区分（until 与not~until的意思区别）.
This is the most important respect______civilized man can be distinguished from primitive communities.
首先确定此题为定语从句,关系词用什么,一般思路为把现行词放在定语从句中考察,同时联系关系词的用法选择即可：此句中现行词为the respect 带入定语从句中可得civilized man can be distinguished from primitive communities (in this respect).故此处可用in which或where引导.