现在完成时，表示从过去某个不确定的时间开始，到现在为止已经完成的动作，并对现在造成一定的影响。
一、结构
肯定句：主语+助动词have(has)+动词过去分词。
否定句：主语+助动词have(has)+not(haven't, hasn't)+动词过去分词。
一般疑问句：Have(Has)+主语+动词过去分词+?
特殊疑问句：疑问词+have(has)+主语+动词过去分词+?
二、用法
1.表示说话之前已完成的动作，而且这个动作的结果对现在是情况仍有影响。常被just, already, yet等副词修饰。
《剑桥雅思真题5》Test 3 Passage 3
Applications of AI have already had a degree of success.
人工智能的应用已经取得了一定程度的成功。
《剑桥雅思真题8》Test 4 Section 3
Have you managed to get the money for the course yet?
你已经设法筹到修这门课的钱了吗?
2.现在完成时还可用来表示过去发生的动作一直延续到现在，常带有for或since等表示一段时间的状语。
《剑桥雅思真题6》Test A Section 3
In the USA, industrial production has risen fourfold since 1950.
在美国，工业生产自1950年以来增长了四倍。
3.在表示“最近几世纪/年/月以来……”时间状语中，谓语动词用现在完成时。
包括：in the past few years/months/weeks/days, over the past few years,during the last three months, for the last few centuries, through centuries,throughout history等。
《剑桥雅思真题4》Test 2 Passage 1
A similar approach in Hawaii has produced about 8,000 new speakers of Polynesian languages in the past few years.
在过去几年里，在夏威夷，一个类似的方法已经产生了大约8000名新的波利尼西亚语使用者。
《剑桥雅思真题10》Test 3 Passage 1
In most industrialised countries over the past few years the fastest growth has been seen in the area of services.
过去几年，在大多数工业化国家，服务业增长最快。
4.表示“第几次做某事”或在“It is the best(worst, most interesting)+名词+that”后面跟现在完成时。
《剑桥雅思真题1》Test 2 Section 1
The only chance I have really had to talk to them was on the field trip.
我唯一能和他们交谈的机会就是在实地。
5.have/has been to+地点表示“曾去过某地”，暗含目前已不在该地，仅表示当事人的一种经历而已。
have/has gone to+地点表示“到了某地去了”，暗含“已离开原地去了某地”之意思，但是否到达了某地尚不确定。
《剑桥雅思真题4》Test 1 Section 3
I have been to the library several times, and all the books are out.
我去过图书馆好几次了，所有的书都借出去了。
《剑桥雅思真题13》Test 8 Section 2
Go up there and it's on your right—if you get to City Road you have gone too far.
上去，它就在你的右边——如果你走到城市路，你就走得太远了。
6.标志词：常见的有ever(曾经), never(从不), so far, up to now,lately, recently等。
《剑桥雅思真题6》Test 1 Speaking Part
Has anyone ever taught you to dance?
有人教过你跳舞吗?
《剑桥雅思真题5》Test 2 Section 2
So far we have provided 46,000 people with bikes.
到目前为止，我们已经为46000人提供了自行车。
《剑桥雅思真题6》Test 1 Passage 1
Up to now no nation has replicated its all-encompassing system.
到目前为止，还没有一个国家复制其包罗万象的体系。
《剑桥雅思真题10》Test 4 Passage 3
More recently, however, examples have been reported that break the time limit, suggesting that silent genes may not be the whole story.
然而，最近有报道称，一些基因突破了时间限制，这表明沉默的基因可能不是问题的全部。
