loading现在完成时
The Present Perfect tense
定义：
1.现在完成时表示过去发生或已完成的动作对现在造成的影响； I have already had breakfast.（我已吃过早餐，我不饿了）
2.现在完成时态还表示过去某一时间已经开始并一直持续到现在（还有持续下去的可能）的动作或状态，可以和表示延续的时间状语连用表示持续的动作或状态的动词多是延续性动词。 We have lived here for ten years.
我们已经在这里住了10年了。（从过去一直到现在都住在这里，并且还会一直持续）
主语 + have/ has + 过去分词（pp）
1) 表示到现在为止已经完成或刚刚完成的动作。 eg1：Now we have planted all the trees.
我们现在刚把所有的树种好。 eg2: He has just come back. 他刚刚回来。
eg3:They have built many buildings in this city. 在这个城市里，他们已经建造了很多建筑物。
2) 表示过去发生的动作,强调结果或对现在的影响。常与just、already、yet连用。
eg1：Someone has broken the window. (窗户现在是坏的) eg2: I have already lost the key. (我现在没有钥匙) eg3: I haven’t read that book yet . (不了解书的内容) eg4: I have just cleaned my hands. (手是干净的)
※常与already(已经), yet(已经), just(刚刚),ever(曾经),never, for+时间段，since+时间点 等词或短语连用. ※already: 常用于肯定句中. yet: 常用于否定句,疑问句尾.
3) 表示从过去开始并持续到现在的动作或状态，常与for和since等表示一段时间的状语连用。
She has learned English for 5 years. for + 时间段 He has lived in Beijing since 5 years ago. since+ 时间点
注意：
1) 现在完成时不能单独与过去的时间状语连用yesterday, last week, three years ago 等; 2)不能与when连用
since: (自…以来) 1)since+时间点
He has stayed here since 5 o’clock. 2)since+ 时间段+ ago
He has stayed here since 5 hours ago. 3)since+ 从句 She has taught English since he came here. for: (长达） for+ 时间段 He has kept the book for 2 weeks.
练习1 用for 或since填空
1. Mr. Brown has had his TV ______ 15 years. for
, 如2. I’ve taken driving lessons _______last month. since 3. My sister has had her cell phone ______a month . for 4. My friends haven’t visited me ______few days ago. since 5. We haven’t used our car _____ a long time . for 6. She hasn’t had a good cup of coffee _____years. for 7. Tom has worn glasses _______he was 7 years old. since 疑难点
I worked here for more than twenty years. (我现在已经不在这里工作了)
I have worked here for more than twenty years. （现在我仍在这里工作）
My father has gone to Shanghai for a meeting. 他（已经）去了上海。
My father has been to Shanghai for a meeting. 他（曾经）去了上海。
have been to someplace. 曾经去过某地，已经回来． has gone to someplace.某人去了某地，还没有回来．