3．15．Three students are talking about how to reduce the unnecessary waste in daily life． 16．Wang shen went back to the classroom again because the lights were still on． 17．Wang shen gives us two ideas on how to save electricity in the class． 18．Zhao Xin used to waste a lot of water when she washed her face． 19．Zhao's mother suggested that we should grow plants with the water we used． 20．Pan finds that many people in his dad's office make full use of printing paper．
