--- Do we have to wait for him?--- No, it no difference whether he will come or not.
7. Our older generation used to advise us not to build ____ in the air, but that’s not realistic at all.
8. Usually passengers are required to arrive at _____ one hour before ______ takes off.
9. Which of the following is not a flying machine?
10. As middle school students, raising pet ______ all day long is a sheer waste of time.
11. Don't judge a person only by his _____.