现在完成时中几个标志性词(组)的讲解与演练
我们都知道，现在完成时常见的标志词包括以下词语：just，ever，never，yet，already，for，before，since，so far，recently，twice，three times等。
虽然同为标志词，但它们的用法却不尽相同。
这里试就其中几个易混淆的词做一简要讲解，供同学们学习参考：1.ever，never：ever意为“曾经”，本身为肯定意义，可用于肯定、否定和疑问句中；never意为“从不”，本身具有否定意义。
1) Have you ever seen that kind of animal?你以前曾经见过那种动物吗？
2) I have ever been to London.我曾经去过伦敦。
3) No one ever known the news about him.没有人知道有关他的消息。
4) She has never told us about herself.她从未告诉我们有关她的事情。
2. already，yet：二者都有“已经”的意思，但already常用于肯定句的中间，yet则多用于否定、疑问句末，常表示“已经，还没有”。
1) I have already had lunch.我已经吃过午饭了。
2) ----Have you finished your homework yet?你已经完成你的作业了吗？----No, not yet.还没有。
3. for，since：如果想表达“我在北京已经居住了10年”这个意思，既可以说: I have lived in Beijing for 10 years. 也可以说:
I have lived in Beijing since 1996. 也就是说, for 表示“到......的数量”，常和一段时间连用；而since表示“自从......以来”, 其后常跟过去某一起始时间点或过去的动作。
又如: The boy has studied all the time since he came into the room.
4. before：“以前”, 在现在完成时中，一般放在句末。
1) I think I have met you before.我想我以前见过你。
2) It seems that I have been here before.我似乎以前来过这里。
实战演练：
一、用括号中动词的适当形式填空：
1. ______she ______ (wait) for an hour yet?
2. He______(not finish) the work yet.
3. Li Ming _______(know) him since then.
4. I ______(receive) a letter from my brother recently.
5. We ________ (be) there many times.
6. How long ______ you _______ (learn) English?
7. Wang Ming _______ (not read) the book before.
8. --He _________ (live) in this city since he ________ (leave) his hometown.
--When did he ________ (leave) there?
--He ________ (leave)there three years ago.
9. --His father _____ (be) in the Party for years.
--When _____ he ________ (join) the Party?
--He _______ (join) the Party in 1996.
10.-- It ______ (rain) for such a long time!
-- When _______ it _______ (rain)? --It _____ (rain) 3 hours ago.
二、根据中英文提示完成句子。
1. 我爸爸已经工作了25年了。
my father, work, for , 25 years
________________________
2. 你学英语有多久了？how long, you, learn, English
______________
3. 他自上中学就买了这辆自行车。
he, have, bike, since, study, middle school
_________________
4. 这本书我已读了一个月了。
I, read, book, for, a month
___________________
5. 这星期他已经去过图书馆三次了。
He, be, to, library, three times, this week ____________________。