We should__________ _________,and we can’t _________ it.
4.树有助于空气清新,我们应该保护它们。Trees can ___________keep the air __________,and we should ________ them.
5.海报准备好了,让我们把它放在校门口。The poster is __________ , and ___________ put it at the school __________.
6.我们用木头制成桌子。We ________ _______ _______ _______ tables.