Thanks for your tips. I also understand all the tips from you. To be frank, i was working in a international school for 8 monthes. I need to speak english everyday with those foreigners. But i don't why sometimes i still can't understand what other people said completely. So i resigned this job and found another job. But it's so ridiculous because this job still need i speak english everyday. So i am looking for some friends who can improve my english and corret my mistakes on line. I read your profile and know you can speaking chinese.