这两个词都可以表示“能够”。can通常用来表示现在的一般能力。如：Look, I can do it.嗨，我会做这事啦。而当表示将来能力时，一般要用will be able to。此外，be able to 还表示要经过一番努力才能做到的事。如：If I concentrate on the work, I'll be able to work out the problem.如果我集中思想于工作的话，我就可以想出这个问题的解决方法。I'll be able to speak French in another few months.再过几个月我就可以说法语了。
2、call on, visit
call on：“拜访”，为社交用语，强调较正式的访问。如：I hope to call on you at your office at three o'clock today.我希望今天下午三点钟到办公室去拜访你。
visit：“访问，参观”，指为一定目的去访问某人或参观某地。如：Professor Li is often visited by his students.学生们常去看望李教授。
注意：call at与call on都可以作“访问”解，但call at后接地点；call on后接人。如：I called at the bank and drew some money today.今天我去银行取了些钱。
3、centre, middle
centre“中心”，指圆和球体的中心点并可用作比喻，指事物或活动中心。如；He placed the flowers in the centre of the table.他把花放在桌子的中央。At the centre of the park there is a monument in memory of the hero.在公园的中央有一个英雄纪念碑。London is the political, economical and cultural centre of Britain.伦敦是英国政治，经济和文化中心。
middle：“中间”，指空间或时间意义上与两端等距离的中间部分。如：He telephoned me in the middle of the night.他半夜给我打来电话。Soon they were in the middle of the river.不久他们来到河中央。
4、chance, opportunity
chance表示“机会；可能性（强调偶然性）”，如：If we can swim, the chances are that we can save our lives.如果我们会游泳的话，我们就有可能得救。Harold has lost a lot of money so he wants to take a chance on stock exchange.海洛得丢了很多钱，因此他想在股票上碰一碰运气。
而opportunity表示机遇（强调好时机），既可作可数名词又可作不可数名词。如：This has been my only opportunity to practise speaking English.这一直是我练习英语口语的唯一机会。I am very glad to have had the opportunity to talk to you.我很高兴能有机会与你交谈。
5、certain, sure
certain表示“有把握的，确信的”，语气较强，主语可以是人也可以是物，表示有充分的信心。有时也有“某些”的含义。如：It is certain that the temperature will rise.气温一定会上升。He is certain to come.他一定会来。
sure“确信的，无疑的”，作此义解时，主语常为人而不是物。如：He is sure to succeed.他一定会成功。注意：certain和sure在接不定式和of短语时意思上有差别。试比较：They are certain/sure to succeed.他们一定会成功。They are certain/sure of success.他们有成功的把握。第一例用不定式表示说话人对某事的推断，有“一定，必然”的含义；第二例用of短语表示主语本人的信念，有“确信，对...有把握”的含义。再如：The strike is certain/sure to take place.罢工必然会发生。They are certain/sure of victory.他们确信会获得胜利。
6、care about, care for
这是两个动介型短语动词，后接名词或代词作其宾语。在表示“为...担忧”的意思时，两者可交换使用。
care about主要用来表示“对...感兴趣；关心；在乎”的意思。如：I don't much care about going.我并不很想去。I don't care about what people think.我不在乎人们怎么认为。
care for则主要用来表示“喜欢，对...中意”和“照顾”等意思。如：She doesn't seem to care for him.她好像不喜欢他。Small children are well cared for in nurseries when their parents are working.当父母在工作时，孩子们在托儿所里受到良好的照顾。
7、carry on, carry out
carry on意为“进行，继续”，强调一个行为的进行过程。它可以不跟宾语，也可接表示“工作，讨论，竞赛，战斗”等一类的名词作宾语，相当于continue。它另可作“经营”解，相当于manage。如：Don't let me interrupt you, just carry on.别让我打断你，请继续。I'll try to carry on the work in spite of difficulties.尽管有困难，但我还是会继续这项工作。Rising costs make it hard to carry on the business.成本上升给生意经营带来了困难。
carry out意为“进行，贯彻，实现”，含有按照某个要求或准则进行的意思。它必须接宾语，且宾语往往是表示“工作，活动，职责，命令，计划”等一类的名词。此词语相当于put into practice。如：I have some difficulties in carrying out her order.我感到执行她的命令有些困难。The government was trying to carry out the policy of family planning.当时，政府正尽力贯彻“计划生育”政策。
8、catch up with, keep up with
catch up with为“赶上（某人或某事）”，有追上并可能超过的含义。如：We'll do out best to catch up with the advanced industrial countries.我们将尽力赶超先进的工业国家。
keep up with作“不落后于（某人或某对手）”解，有与之并驾齐驱的含义。如：The girls had to run to keep up with the boys.这些女孩子不得不加快脚步以赶上男孩子们。
9、cause, reason
cause指造成一种事实或现象的“原因”，尤指自然原因或客观原因。如：What's the cause of his success?他成功的原因是什么？
reason指说明一种看法或行为的“理由”，它往往是通过逻辑推理得出的。如：Give me your reasons for refusing.给我你拒绝的理由。This is the reason why he killed the woman.这就是他杀掉那个女人的原因。
10、clothes, clothing, cloth
这三个词都与人们穿的“衣”有关，但含义却不同。clothes永远以复数的形式出现，指人们穿的各种衣服包括裤子，内衣，衬衫等；其前不能用数词修饰。如：These clothes are new.这些衣服是新的。Do I have to change my clothes for the meeting?我去参加会议要换衣服吗？
clothing是集体名词，为衣物的总称，是一种区别于其他事物的概念。除了衣裤之外，它还包括帽，袜，手套，被褥之类的东西，如：The shop sells articles of men's clothing.这个商店卖男式服装。In winter, children need warm clothing.冬天，孩子们需要暖和的衣服。
cloth一般用作不可数名词，指“棉布，毛织品”；它亦可作可数名词，指“某一特定用途的一块布”，复数形式是cloths。如：He will take three yards of cloth to make a suit.他做一套衣服要三码布。She cleaned the window with an old cloth.她用一块旧布擦窗户。
main多用来形容事物的某一组成部分，表示该部分在重要性、力量、大小等方面超过其 他部分，起着主体的作用。The chief reason for going to school is to learn. 去学校主要是去学习的。The president is chief of the armed force.总统是武装部队的首脑。Our main meal is in the evening.我们的主餐是在晚上。Note down the main points of the speech.请记下讲演的要点。
12、choose, select
choose为“挑选，选择”，使用范围较广，指从众多的对象中挑选，这种挑选取决于个人的意志与判断，不强调客观标准。它所选择的对象可以是不同种类的，可以是有形的或无形的。choose带有最终选定的含义，即表示选定后不再变化。如：In the new department store there is a lot to choose from.在新的百货商店有很多可供选择的商品。He chose Miss Li for his wife.他选李小姐为妻。You have to choose between life and dead.你必须在生与死之间作出选择。
select为“挑选，精选”，语气比choose重，多用于正式场合。它指仔细地，审慎地精选，强调客观性，而不是主观性。它所挑选的对象可以是有形的或是无形的，但一定是同一种类的。如：The best machines were selected and sent to the exhibition.最好的机器被选去参展了。He selected a birthday present for his dear daughter.他为他亲爱的女儿挑选了一个生日礼物。
13、come to one's help, come for one's help
come to one's help表示“来帮某人的忙”，与come to help someone意义相同。如：When they heard my cry, they immediately came to my help.他们一听到我的叫声就赶忙来帮忙了。When one man is in difficulties, ten thousand come to his help.一人有难，万人帮忙。
come for one's help表示“来求某人帮助”，与come to ask someone for help意义相同。如：When he is short of money, he often comes for my help.他缺钱花的时候，他常来找我帮忙。She couldn't solve the problem, so she came for our help.她不能解决这个问题，因而来找我们帮忙。
14、continual, continuous
这两个形容词均可表示“连续不断”的意思，但它们在含义上有区别。continual指某一动作不时重复，重复之间有短暂停顿的含义；还有使人不愉快的含义。如：We are not happy with those continual interruptions.我们对那些不断的打扰很生气。My work has been delayed by his continual visit.我的工作被他频繁的拜访给耽搁了。
continuous指某一动作在一段时间内没有中断的含义，表示“持续不断”的意思。如：We felt tired after two days' continuous flight.经过两天不停的飞行，我们感到很累了。There was continuous fighting on the frontier all day yesterday.昨天一整夜，边界上的战斗没有停过。
15、compare...to, compare...with
compare...to为“把...比喻为，把...比成“，指不同类事物的比较，表示抽象的比喻。compare...with为“把...与...比较”，指两个同类的事物相比较，表示人和人，事物与事物之间异同的程度。Life is compared to a voyage.生命常被比作一次航行。People c
