Tales of the unexplained

m2u1 grammar and usage
present perfect tense & present perfect continuous tense
一、 现在完成时
1、 构成 have/has done
2、用法
i表示过去发生的事对现在具有影响。
1） justin has disappeared, so kelly is very sad.
2） the boy is happy. he has caught a bird.
ii表示过去开始的动作一直延续到现在或者还将持续下去。
1）i have not seen justin since last friday night.
2) daniel has lived in beijing since he came to china.
iii表示动作的确切时间不明确或不重要。此时下列词汇经常和现在完成时连用：already, ever, never, for, just, lately/ recently, since, yet。
1） the boy has already come home.
2） i haven’t heard anything from him yet.
其中，for + 一段时间，since + 某个时间点。
e.g. we haven’t seen him for two days.   we haven’t seen him since last monday.
iv表示到现在为止的一段时间内重复的动作。
1） some villagers say that they have seen ufos many times.
2） i have advised him to give up smokin