Can/ Can/ could 的用法 can , could 能,会 (could 可以看作是 can 的过去式,这两个词除了时态不相同外,在表达意思的许多方 面是相同的。当然 could 也有自己独特的用法。) 1)表示脑力或体力上的能力 Nobody can stop the development of science . 谁也无法阻止科学的发展。 She can sing that song in English.她能用英文唱那歌。 He can submerge to a depth of about twenty meters . 他能潜入约二十米深的水中。 He could hardly support his family before he found the new job .他在找到那份 新工作前几乎无 法养家。 I could not understand the lecture on the computer given by Mr. Smith . 我听不懂史密斯先生作的那个关于计算机的讲座。 2)表示客观上的可能性 You can borrow this useful book from the library . 你可以从图书馆借到这种有用的书。 A more suitable person than him for the job can not be found . 不可能找到比 他更适合这份工作的人了。 Now people can skate on the lake .现在人们可以在湖上滑冰了。 When the storm stopped , the plane could take off . 当风暴停下来时,飞机可以起飞了不得。 3)表示主观上的允许 Can I ask you some questions about it ? 我可以问你有关这件事的几个问题吗? You can not leave here till I come back .直到我回来你才能离开。 Such kind of thing can't happen any more later . 这类事以后不准再发生了。 Can you tell me how to get to the airport ? 你能告诉我怎么去机场吗? Could you tell me how to get to the airport ? 您能告诉我怎么去机场吗? Could I be forgiven my negligence ? 请原谅我的疏忽,行吗? 4)(用于否定句、疑问句或感叹句中)表示猜测、怀疑或惊诧 How can / could you be here ? 你怎么会在这儿? She couldn't / can't be so stupid to do that . 她不可能蠢得去做那种事吧。 He couldn't / can't be over seventy .他不可能有七十多岁了。 Where could / can the boy be now ? 那孩子现在能在哪儿呢? 另外, could 还常用于表示较客气委婉的看法、 提问及用于虚拟语气的结构中。 这时候, could 就不可以看作是 can 的过去式了。而是 could 自己独特的用法。如: Could you speak a little slowly ? 您能稍微说慢一点儿吗? I'm afraid that we couldn't give you any definite answer at this moment . 恐怕我们这时候还无法给予您任何确切的答复。 I could come earlier if asked . 如果要让我早一点来,我可以来早一点。 We would appreciate it if you could offer us any help . 如果您能为我们提供帮助的话,我们将不甚感激。 You could have done better if you had worked harder at it . 如果你再加把劲,本来可以干得更好一些的。
现在完成时两种时间状语现在完成时属于现在时范围,故不能和表示过去的时间状语连用,如:yesterday, last Sunday,in1990,three years ago等。它的时间状语有两种情况,下面我们就来区分一下它们。 一、表示结果的副词用作现在完成时的时间状语 1.already和yet。already一般用于肯定句中,yet一般用于否定句和疑问句中。例如: We have already finished our homework.我们已完成作业了。 2.ever 和never。多用于否定或疑问句中,表示“曾经”或“从未”等。例如: ―Have you ever been to the Great Wall? 你曾经去过长城吗? ―I have never been to the Great Wall.我从未去过长城。 3.用表示到说话为止的过去时间状语,如just, before, up to now, the past/lastfew years等。例如: I have seen her before, but I can not remember where. 我以前见过她,但记不起在哪里见过。 4.用包括“现在”在内的时间状语,如:now, today, thismorning(month, year, term)等。例如: ―Have you met him today? ―No, I havent. ―今天你见过他吗?―我没有。 二、表示动作延续的for,since用作现在完成时的时间状语 现在完成时可以与since或for等表示“一段时间”的状语连用,表示动作或状态从某一时刻开始,一直持续到现在。如:I havent seen him for two years. 但是,像come, arrive, buy等终止性动词不能与表示“一段时间”的状语连用。如要用,必须改为“be(在)”等延续性动词来表述。现归纳总结一下由非延续性动词到延续性动词的转换:arrive→ be here,begin(start)→be on,die →be dead,come back→ be back, leave →be away,fall ill(sick,asleep)→ be ill(sick, asleep),get up→ be up,go out