用方框中所给单词或短语的适当形式填空

build; in great danger; play a part; have to; peaceful

【1】All of us should _________ in planting trees.

【2】Elephants are _________.We should do something for them.

【3】Most people in the world love _________; they don't need war(战争).

【4】We will _________plant more trees in order to protect the earth.

【5】_________more highways will help the environment by reducing pollution and traffic jams.