拓展：have been，has been， had been
1.解释：have/has/had+been 都是完成时。
2.区别：has/have been是现在完成时,has用于第三人称单数; had been过去完成时,跟前者相比,比前者更为过去;
3.例句：
（1）He has been doing this work for a period of time.
（2）I want to have this book.
（3）Have you pass the math exam?
（4）Do you ever had a thought that you can win this game?
