现在完成时用法
1.描述发生在过去的动作，但不清楚动作发生的具体时间
.
e.g. I have (just) received a letter from my brother.
e.g. He has (just) bought an Australian car.
2.描述一个动作在过去某个时间开始之后一直持续到现在
For,Since
e.g. She has worked here for 3 years.
e.g. She has worked here since 3 years ago/ since 2014.
for+ a period of time.
since+ a specific point in time
3.重点结构
a) since,for
b)I've just,I've already, I haven't .....yet/Have you .....yet?
e.g. Does John know that you're going away?
---No,I haven't told him yet.
e.g. This is my new dress.
----It's nice. Have you worn it yet?
c) Have you ever.......? I have never.....
e.g. My brother has never been abroad before.
e.g. Has your brother ever been abroad before?
d) has gone, have been
e.g. I can't find Susan. Where has she gone?
oh,hello,Susan. I was looking for you.
Where have you been?
e.g. He has just bought an Australian car and has gone to Alice Springs.
4.现在完成时常搭配的时间状语
Up to/till now=so far= since then
Recently=lately
In the last/past few days/ weeks
