根据下列短文内容，在文中空格处填上一个恰当的词，使短文完整、通顺。
The earth is our homeland. We must look after it. Do you think it's our duty to 1 the environment?
Sure, many famous 2 have started living a green life to set good models (榜样) for us. Some people
go to work by bike or 3 foot. Some people often reuse (重复使用) water. For example, 4 they
finish washing clothes, they use the water to clean the floor or water flowers. As for students, we can
also do things to help. Saving(节约) paper is necessary. Try to make full use of 5 . Don't throw away
the used textbooks but give 6 to your brothers or sisters. And if we don't want 7 watch TV, turn it
8 in time. On 9 other hand, we 10 plant trees as many as possible.It's really important to live a
green life, a happier life!