预习导航

　　一、阅读课文"HOW LIFE BEGAN ON THE EARTH"并回答下列问题

　　1．What is the right order according to the text?

　　①Animals appeared and spread.

　　②The formation of the earth.

　　③Plants appeared.

　　④Difference between the earth and other planets.

　　A．②-③-④-①　　　　B．②-④-③-①

　　C．③-④-①-②　　　 D．②-①-④-③

　　2．Why was the earth different from other planets?

　　A．It produced a lot of heat.

　　B．Water remained.

　　C．Water disappeared.

　　D．It was the oldest planet.

　　3．What is the main cause that life was able to develop on the earth but not on other planets?

　　A．The earth had a solid shape.

　　B．The earth did not have harmful gases in its atmosphere.

　　C．Water stayed on the earth but not on other planets.

　　D．The earth was neither too hot nor too cold.

　　4．Why was it necessary for plants to grow before animals?

　　A．Animals needed plants to protect them from the sun.

　　B．Plants provided oxygen for animals to breathe.

C．Animals could hide from hunters in the forest.