can与be able to
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。call on与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。
care about与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。
carry on与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。
catch up with与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。
cause与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。
centre与middle
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 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。certain与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。chance与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。
cheap 与cheaply
两者均可表示“便宜地”、“廉价地”，但前者主要与表示“买”（如buy, get, pick up等）或“卖”（如sell）之类的动词连用，且置于其后；后者用法较广，可置于动词之前或之后。如：
He sold it cheap [cheaply]. 他卖得很便宜。
The radio was cheaply bought [was bought cheap]. 这收音机买得很便宜。
The room was cheaply furnished. 屋里配置了便宜的家具。
The bus takes you there cheaply. 坐公共汽车去便宜。
We mustn’t sell our goods so cheaply. 我们的货不应该这样便宜地卖。
I got them quite cheaply. 它们我买得很便宜。
There you can play golf comparatively cheaply. 在那里打高尔夫球比较便宜。
They told us where to shop cheaply. 他们告诉我们在哪里买东西便宜。
Such vaccine can be mass-produced cheaply. 这种疫苗可以便宜地大批生产
chief与main
这两者都表示“主要的”。chief表示所指的对象在重要性、地位、等级方面高于其他同类事物，暗示其他事
