教材习题点拨

　　COMPREHENDING

　　Answer key for Exercise 1：

　　Paragraph 1：A widely accepted theory about the formation of the universe

　　Paragraph 2：The formation of the earth

　　Paragraph 3：The importance of water for life

　　Paragraph 4：The development of plants and animals on the earth

　　Paragraph 5：The arrival of humans and their impact on the earth

　　Answer key for Exercise 2：

　　10　7　3　8　4　9　6　1　5　2　12　11

　　Answer key for Exercise 3：

　　1 Because the water remained on the earth.

　　2 Because plants provide oxygen for animals to breathe.

　　3 Because dinosaurs died out long before human beings developed on the earth.

　　4 The name is Pluto.Scientists now think it is too small to be called a planet.

　　5 Human beings caused global warming.

　　Suggested answers to Exercise 4：

　　Discourse markers：

　　however，after that，next，later，finally，thus，as a result of

　　Sentence connectors or conjunctions：

　　and，but，because

　　Suggested answers to Exercise 5：

　　The other puzzles hidden in the passage are：

　　How did the earth's atmosphere develop?

　　Why did water stay on the earth but not on the other planets?

　　How did life forms develop?

　　Why did some life forms disappear?

　　LEARNING ABOUT LANGUAGE

Discovering useful words and expressions