Unit 1 Topic 1 Our country has developed rapidly.
Unit 1 Topic 2 The population in developing countries is growing faster.
Unit 1 Topic 3 The world has changed for the better.
Unit 2 Topic 1 Pollution has caused too many problems.
Unit 2 Topic 2 All these problems are very serious.
Unit 2 Topic 3 What can we do at home to protect the environment?
Unit 3 Topic 1 English is widely spoken throughout the world.
Unit 3 Topic 2 Some things usually have different meanings in different cultures.
Unit 3 Topic 3 Could you give us some advice on how to learn English well?
Unit 4 Topic 1 When was it invented?
Unit 4 Topic 2 I'm excited about the things that will be discovered in the future.
Unit 4 Topic 3 China is the third nation that sent a person into space.
