1. A lot of trees have been broken by teenagers.
2. Our rivers has been polluted by factors and plants.
3 The words "I love Helen" have been written on the tree by Tom.
4. A lot of litter have been dropped in the forest by these children.
5. 30 kilograms of waistpaper have been collected by the pupil of 9 A.
1b, 2a, 3a, 4a, 5b, 6c, 7d