废气涡轮增压器的喷嘴环主要作用有（）①提高废气压力②提高废气流速③缓和废气的压力波动

完成对话。
  玲玲要去英国学习，她向她的网友玛丽了解英国的有关礼仪。
     Ling Ling: I'm going to England as an exchange student.
     Mary: Great!
     Ling Ling: But I don't know much of the customs and manners in England. ___1__.   
     Mary: Sure.
     Ling Ling: ___2__.   
     Mary: Well, they think it's important to be on time when you're invited to dinner. __3___. As it is
     usually planned to have the meal at the exact hour.
     Ling Ling: Then how long may I stay there?
     Mary: __4___, it seems that you have come only for the meal. An evening dinner invitation usually 
     implies  that ___5__. The hostess often plans some after-dinner entertainment.