A Listen and number
录音文字稿：
1. We can take the bus or the metro to school.
2. We can go to school by bike.
3. We can plant more trees to keep the air clean.
4. We can put rubbish in the bin.
5. The street is dirty and messy.
6. Black smoke from the factories makes the air dirty.
参考答案：
a 2 b 6 c 5 d 3 e 1 f 4
B Listen and choose
录音文字稿：
1. Please put your rubbish in the bin. We should keep the park clean.
2. Look at your books and toys, Mike. They make your bedroom so messy.
3. There is a lot of rubbish in the river. The river is dirty and the fish are dead.
4. The table is dirty. There is some milk and water on it. Please clean it.
5. To keep the classroom clean, we should sweep the floor every day. We should clean our desks and chairs too.
参考答案：
1. a 2. a 3. a 4. a 5. b
C Read and circle
参考答案：
1. a 2. b 3. c 4. b 5. c 6. c
D Look and say
参考答案：略
E Read and write
参考答案：
1. friends 2. wood 3. Fruit 4. beautiful 5. clean
F Look and write
参考答案：
1. sign, littering, river, bin
2. Smoke, take, metro
3. kitchen, messy, sweep, clean
4. throw, make, keep
