Use the words to complete the text.
nesting boxes, Planting, pollution, voluntary, nests, left
Volunteers also build . It is a very important job as there are not so many trees in big cities for birds to build their own . Volunteers learn about the main causes of air and water___ . trees and flowers is also a significant part of their jobs.
1)eco-helpers
2)recycling
3)clean out
4)volunteers
5)the cycle of life
6)ecology
2 left
3 nests
4 pollution
5 Planting