Supply the correct form of the verb in the bracket:
16. Flowers should ( keep ) in warm places. ......................
17. When I arrived at the camp site, they ( lay ) out the blanket. ......................
18. If I won a million dolars, I ( buy ) my parents a new house. .......................
19. He said that he ( see ) that man before. .......................
20. The candidates ( sit ) for the exam are all from Vietnam. .......................
16 keep
17 were laying
18 would buy
19 had seen
20 sit