15. How……......………. do you visit the zoo? - Once a month.
16. There’re black cloud……......…….…the sky.
17. Put…......……your warm coat. It’s cold day.
18. What do students often do……......……break?
19. I don’t feel like walking. – OK. We’ll go home……......……….a taxi.
20. Marry is not at home now. He is …......…….work.
