15. How often do you visit the zoo? - Once a month.

16. There’s a black cloud in the sky.

17. Put. on your warm coat. It’s a cold day.

18. What do students often do…….....at the.……break?

19. I don’t feel like walking. – OK. We’ll go home……..by....……….a taxi.

20. Marry is not at home now. He is …...working at...…….work.