Exercise 4. Choose the correct word to complete each sentence. 1. We need to plant / build / clean flowers in the park. 2. They collect / recycle / teach cans, bottles and paper every Sunday. 3. Birds need trees to build / clean / plant their nests. 4. Please collect / clean / build out the pond - it's very dirty. 5. Volunteers teach / recycle / plant children about ecology. 6. Don't throw rubbish on the ground - collect / recycle / build it! 7. We are building / planting / cleaning nesting boxes for birds. 8. She is reading / teaching / collecting a book about the environment.