Put the words in the blanks into the correct forms.
16. Be quiet! The baby ___ (sleep).
17. Last weekend, our group ___ (make) many pencil cases from plastic bottles.
18. We have our plan for the summer holiday. We ___ (join) the 3Rs club to help the environment.
19. What is the ___ (high) mountian in the world?
20. If we ___ (protect) the forests, we ___ (help) our planet.