DBBE
1. The introduce of the mission that explored natures on Mars
2. The failure to show the existence of lifes on Mars
3. The new evidence and factors contributed to restart the mission (extremophiles、limitation of Viking's sensors、politically competitive spirit)
4. A vision to the future
p1 viking+探索的方法介绍
p2 viking探索结果==>因为没发现生命,美国放弃探索mars,move on
p3 viking探索中的局限+美俄竞争
p4 mars observer出现,重新探索mars——如今的发展:探索目标不drama
结果:没有证据证明火星是否有生命
1 B
2 D
3 B
4 E