lol封号查询停机:what must you do when your flight arrives at the airport?

what must you do before getting off a train what do you do 脑筋急转弯 What must you do before you return a book to the library? what must you do when your flight arrives at the airport? what do you do 是什么意思? what do you do ???是什么意思? WHAT DO YOU SAY What do you think? what do you like ? What do you mean~~~