It is important to know about the cultural differences that        cause problems.

I want to open the door, but it _____ open.

--Why didn’t you come to Simon’s party last night?---I wanted to, but my mom simply _________ not let me out so late at night.

—A shy boy like John ________ give up a secure job and start his own business!—Yes，nobody had expected that. 

 A mistake ______ have been made on our bill. We didn’t order any fish today.