8 ．for the first time / the first time / the time
for the first time: 在句中作状语；the first time和the time在句中起着连词的作用。
例817：They were invited to the palace ball for the first time in their life .他们被邀请参加他们一生中第一次的宫廷舞会。
例818：It was for the first time that he made such a mistake .他第一次犯了这样一个错误 强调句型
例819：It is the first time that he has made such a mistake .这是他第一次犯这样的错误。
例820：The first time I met him he was feeding his sheep .我第一次见到他时，他正在喂他的羊。
此处语法意义上可以用the last time 最后一次或 the next time下一次,替换
例821：The time the bell rang all the pupils rushed out .铃声一响，所有的学生都冲了出来。
此处语法意义上可以用as soon as the moment the minute the instant instantly immediately一…就…;等替换；还可以用Hardly … when Scarcely … when no sooner than等倒装结构来表达。
例822：Hardly had the bell rang when all the pupils rushed out 铃声一响，所有的学生都冲了出去。
It is the last time I will take on this sort of,work .这将是我最后一次干这种工作了。
I can't remember the last time we went to the cinema .我记不得上次我们去看电影是什么时候了。
He told me the next time you and I met to give it to you. 他告诉我下一次我和你见面，把这个给你。
9 ．in all / at all / after all / above all / for all / first of all
in all：总计 =in total 。at all：根本，全然 用于加强语气 。after all：毕竟。above all：首要 相当于the most important of all 。for all：尽管。first of all：首先。
例823：First of all ,I’d like to share the good news with you . 首先，我想和大家一起分享好消息：
For all the difficulties, we’ve managed to finish forty items in all .尽管存在种种困难，我们还是设法完成了总共四十个项目。
But we still have to work harder ,and above all ,we shall value every possible minute .然而，我们还得更加努力，最重要是要珍惜每分每秒，
After all we have only ten days to go , We have no time to waste at all! 毕竟我们的期限只剩十天，我们的时间实在浪费不起啊！
10 ．in the end / at the end of / by the end of
in the end：最后，终于。指时间，相当于at last或finally。
例824：He waited and waited ,but gave up in the end .他等了又等，但最后还是放弃了。
at the end of：在……末了，在……末端。指时间或地点。
例825：At the end of the party they added another program .晚会结束时，他们又增加了一个节目。
例826：You’ll find the post-office at the end of the street .你可以在街的尽头找到邮局
by the end of：在……结束时，到……末为止。常用完成时态。
例827：We had learnt twenty-four units by the end of last term .到上学期末我们已经学了二十四个单元
例828：We will have learnt twenty-four units by the end of this term .到本学期末，我们将学习二十四个单元
11 ．in the past / in the past three years
in the past：过去 用过去时 。in the past three years：近三年 用现在完成时 。
例829：Our town was poor in the past but great changes have taken place in the town in the past / last three years 我们的镇过去穷，可是近三年发生了翻天覆地的变化。
1 ．because / since / as / for
because：因为。表示直接而明确的原因或理由，语气最强。
例830：It was because he got ill that he didn’t come .是因为他病了才没有来
since：既然。表示说话者和听话者双方都明白的原因，相当于now that。
例831：Since you see my point let’s start right away . 既然你明白我的意思，那我们开始行动把。
as：因为，既然。语气不如because那么强。
例832：As he is so mean nobody around likes him 他吝啬，身边没有一个人喜欢他。
for：因为。语气最弱，只是解释性的，没有直接的因果关系；它是并列连词，不用于句首。
例833：It must have rained，for the road is wet 想必下过雨了，因为道路湿着呢。
2 ．if / whether
if和whether都有“是否”的意思。whether可以引导主语从句、宾语从句、表语从句和同位语从句，if则只能引导宾语从句且不放在句首；whether后可以接to do结构，if 则不可以。另外，if有“如果”的意思，引导状语从句。
例834：Whether they will come on time is still unknown .他们是否会按时来还不确定
例835：We don’t know whether they will come on time . We don’t know if they will come on time .我们不知道他们是否会准时来。
例836：We don’t know whether to come or not .我们不知道是来还是不来
例837：If they come ,we’ll tell you at once 如果他们来了，我就马上告诉你。
3 ．though / although / even though / as though
though：虽然 用作连词，引导状语从句；也可用在倒装结构中 ；然而 用作副词，一般放在句末 。
例838：Though it was very late ,he went on working .尽管很晚了，他还是继续工作
例839：Young though he is , Though he is young ,he knows a lot .虽然他年轻，但他知道很多
例840：He said he would come， he didn’t though . 他说他会来，但他没有
although：虽然。不用作副词，不用在倒装结构中。
例841：Although it was so cold ,he went out without an overcoat .尽管天气很冷，他还是没有穿大衣出去了。
例842：He is quite strong, although very old .他很强壮，虽然很老。
even though：即使。等于even if。
例843：I wouldn’t attend his party even though invited to .我不会参加他的聚会，即使被邀请参加
as though：好像。等于as if。
例844：He runs as though he were mad 他跑起来像发疯似的。