He didn't know _____ when his mother wasn't at home.A.how should he do B.what should he doC.what to doA.how是肯定不对的.分析语句看是to do "what"还是"how".句意是表达这人的无所事事而不是具体到某件事情怎么做,所以是What。B.那么这个选项是What了,选么?不选。因为如楼上的楼上所说,应该是He didn't know what he should do...才对。What should he do?已经是一个问句了,在从句中要注意倒装。C。对的。what to do 就表示了一个将来的时态。to do what 的倒装。做这种题懂语法当然可以做出来,不懂得话就像现在教育提倡的语感来做也可以的。(一) 正误辨析 1、[误] We got to the top of the mountain in daybreak. [正] We got to the top of the mountain at day break. [析] at用于具体时刻之前,如:sunrise, midday, noon, sunset, midnight, night。 2、 [误] Don't sleep at daytime [正] Don't sleep in daytime. [析] in 要用于较长的一段时间之内,如:in the morning / afternoon, 或 in the week / month / year. 或 in spring / supper /autumn / winter等等。 3、 [误] We visited the old man in Sunday afternoon. [正] We visited the old man on Sunday afternoon. [析] in the morning, in the afternoon 如果在这两个短语中加入任何修饰词其前面的介词都要改为on, 如:on a cold morning, on the morning of July 14th 4、 [误] He became a writter at his twenties [正] He became a writter in his twenties [析] 这句话应译为:他在20多岁时就成了作家。在某人的一段生活时间段中要用介词in来表示,而在具体岁数时用at来表示。 5、 [误] He went to New York to find a job in sixteen years old. [正] He went to New York to find a job at sixteen. [析] 在具体年岁前用at, 如:at the age of 12, at your age, 等等。 6、 [误] We went to swim in the river in a very hot day. [正] We went to swim in the river on a very hot day. [析] 具体某一天要用介词on, 又如:on New Year's Day7、 [误] I'm looking forward to seeing you on Christmas. [正] I'm looking for ward to seeing you at Christmas. [析] 在节日的当天用on,而全部节日期间用at,Christmas是圣诞节期间,一般要有两周或更长的时间。 8、 [误] I haven't see you during the summer holidays. [正] I haven't seen you since the beginning of the summer holidays. [析] during表示在某一段时间之内,所以一般不与完成时搭配,如:I visited a lot of museums during the holiday. 而for表示一段时间,可以用于完成时,如:I haven't see you for a long time. 而through 用来表示时间时则为"整整,全部的时间"。如:It rained through the night.而since则是表达主句动作的起始时间,一般要与完成时连用 9、 [误] At entering the classroom, I heard the good news. [正] On entering the classroom, I heard the good news. [析] On 加动名词表示"一……就"。本句的译文应是:我一进入教室就听见这个好消息了。又如:on hearing… 一听见, on arrival 一到达就……(on表示动作的名词) 10、 [误] In the beginning of the book, there are some interesting stories. [正] At the beginning of the book, there are some interesting stories. [析] at the begining与at the end都是指某事物的开始与结束部分,均不指时间范围,而in the beginning 则是指开始一段时间。in the end=at last是指"最终,终于"之意。 11、[误] Till the end of next week. I will have finished this work. [正] By the end of next week. I will have finished this work. [析] by 引起的时间状语表示了动作的截止点,其意思为"不迟于某一时刻将工作做完",大概出一点 希望对你有帮助