[观察例句]
1．People have been enjoying the benefits of cycling in Amsterdam for years.
2．Many people around the world have been enjoying city centre streets without cars for many years.
3．He has been fighting with a friend.
4．I have been looking for a job for three months.
5．I have been writing letters all this evening and I've just finished them.
6．You haven't been doing your homework those days.
