大学英语：现在完成进行时

1.基本用法
　　从过去某时起一直持续的动作，一般是为了强调动作正在进行或反复。
　　I have been washing all morning.
　　He’s been watching television all day.
　　2.基本结构
　　现在完成时S+have(has)+动词过去分词
　　（现在完成进行时）+S+have(has)+been+动词ing，其否定，疑问变化。
　　3.特点
　　(1)其多与how long或long、all一起用。
　　All night long this has been going on.
　　How long have you been reading that book?
　　(2)有时表示的是动作的反复而非一直在持续。
　　We’ve all along been making mistakes like this.
　　Has it been causing problems?
　　(3)现在完成时常常倾向动作业已完成。
　　现在完成进行时大多都表示动作还在进行或反复。
　　She has painted her room.
　　She has been painting her room.(可能还未漆完)　I’ve read a book.
　　I’ve been reading a book.
　　(4)有些静态动词只能用于现在完成时，一般不用于现在完成进行时。
　　I’ve known him for many years.
　　They’ve been married for 50 years.
　　This has lasted for a long time.
　　(5)在强调动作持续时间的长度时，特别是有long、how long这类状语时，常用现在完成进行时。