demand, request, require
1.demand主语是人时，表示坚决要求，坚持要做某事；主语是物时，指迫切需要。
Request意为“恳求，请求”，指通过正式手续提出的要求，口气和缓，态度礼貌。Require表示按照法规、权利提出的要求或命令，指客观需要，含缺此不可之意。
Cement is in great demand.水泥的需要量是很大的。
He demanded an apology from them.他要求他们道歉。
All I requested of you was that you came early.我对你的唯一要求就是早点来。
I have done all that is required by law.我已做了法律规定的一切。
The situation requires that I should be there.形势需要我呆在那儿。
2.后面跟宾语从句时，从句后谓语动词都要用虚拟语气，即should加原形动词或动词原形。例如：
The teacher requested that each of us(should)go there at once.老师要求我们每一个人要马上到那儿去。
The teacher required that all of us(should)attend the meeting.老师要求我们大家都出席这次会议。
The teacher demanded that Mary(should)give a right answer.老师要求玛丽给一个正确的答案。
3.request后接sb. to do sth., demand后接of sb. to do sth., 而requre后接两者均可。例如：
Mr.White requested his daughter to leave here.怀特先生要求他的女儿离开这里。
Mr.Green required his students to keep silent.（=Mr. Green required of his students to keep silent.）格林先生要求他的学生保持安静。
He demanded of me to shut the gate.他要求我关上大门。
故若把上面2中的三个含虚拟语气的宾语从句改为简单句时，应分别为：
The teacher requested each of us to go there at once.
The teacher required all of us to attend the meeting.
The teacher demanded of Mary to give a right answer.
4.require表示“需要”的意思，后可接动词不定式或动名词。接动词不定式时，应该用不定式的被动形式，接动名词，时，用动名词的主动形式（表示被动意义）。
例如：
The baby requires to be looked after. =The baby needs/wants to be looked after. =The baby requires/needs/wants looking after.
注意：
①require(of)sb用于被动语态时，of不可省。如：
I have done everything that was required of me.
②demand后接from sb或of sb.
He demands help from/of me.
③demand后接不定式，不接动名词。
He demands to see my books.
