道格拉斯生产函数模型

It ( )Mike and Mary who helped the old man several days ago. A.was B.were C.are D.had been答案是A,说是指代整件事.能解释一下,再举个选B的例子么 IT WERE MIKE AND MAY WHO HELPED THE OLD MAN SEVERAL DAYS AGO为什么用WERE不用WAS 【选择】50.it （ ）Mike and Mary who helped the old man seveal day ago.（ were / was / are / had been）这题选什么,理由是. She __(visit)China befor Has she visited China before?为什么用现在完成时?参观是一个动作,为什么不用一般过去时呢?还是要结合语境? barren很多解释,最常用的是哪个意思?不要复制词典解释 “我是来日常的”是什么意思? desirable最常用的意思是什么麻烦大家只要一个意思 最常用的就好 U can touch my body什么意思这什么意思?250分! 英语翻译谁知道呢来顶下谢谢大侠们! you should close the window after you go out and_____it when you are back. do you remember —— （close） the window before we came out? 传统教育的主要思想是什么? 人们常用“苍耳”比喻什么?或什么样的人（精神要有积极意义） Shirley( )a book about China last year but I don't konw whether she has finished it.A.has written B.wroteC.had writtenD.was writing要有理由.而且最好能够说明它考的是哪方面的知识点. 请教一道英语自考语法反义疑问句的题目：You'd rather I didn't tell her the new,对应的反义疑问是什么? 天空没有留下痕迹,但鸟儿已经飞过 英语翻译这句话 Ten years ____ passed.A.have D.has一段时间,视为单数.所以动词要用单数 可为什么答案是 have Ten years have passed ( ) he moved to live in the South.可选:A.fromB.whenC.since 什么叫道德涵养,怎样才能有道德涵养 为地球列几条保护措施 怎样为地球列几条保护措施 英语翻译要地道一点的英文表达`````英文高手快来 英语翻译能帮我翻译成英文吗 翻译成英语:虽然天空没有留下任何痕迹,但是我已经努力地飞过. what is Tom保持原句意思 （ ）Tom is （what is Tom保持原句意思（ ）Tom is （ 涵养可形容一个教师吗 形容一个人有知识有涵养该用什么形容词好 Three years passed是什么意思 我一个朋友想在北京当一名初中历史教师,实习过.应该如何找一份教师的工作?去人才市场吗?还是什么别的途径?越详细越好.复制粘贴的全PASS.一定要本人亲自回答....您发的小心我今天晚上才 Although a teenager,Tom could resist ____what to do and what not to do.Although a teenager,Tom could resist ___what to do and what not to do.A.being told B.thinking C.to be tempted D.on trying 请帮忙选择并讲一讲理由! what can Tom do?can后面三单还用动词原型吗?不是what can Tom does?