16. Astronauts_______________in their spaceship, but they frequently work outside now.

A. were used to stay       B. used to stay            C. use to stay                D. used to staying

17. People __________________that the earth is round before.

A. were not used to believe        B. used to believing      C. use to believe        D. did not use to believe

18. Mr Kim________________________a secret police before.

A. use to be thought         B. used to be thought        C. used to think           D. use to think

19. A lot of children_________________from dead in the second war.

A. get used saving         B. used to save        C. used to be saved       D. used to saving

20. These girls are used______________________in the field.

A. to work                     B. to working                C. worked                              D.working