The main trouble is that our neighbor worlds, the bodies in the Solar system appear to be unsuitable for advanced life-forms. The Moon may be ruled out at once; it has hardly any atmosphere. Venus(金星) is little better; the surface temperature is extremely high and the atmosphere is mostly carbon dioxide. Mars with a very thin atmosphere and a severe shortage of water, may well support simple plant life but there seems no hope of finding animals, while the attractive Martians(火星人) of the story-tellers have long since been given up.
Of course this has not stopped the flow of bright ideas for communicating with the supposed people on Mars. In the early nineteenth century the great mathematician Gauss suggested planting treepatterns in Siberia(西伯利亚), so that the Martians would see them and replay suitably. Following up this idea, the Austrian scientist Karl Littrow proposed digging very wide ditches in the Sahara, triangular in patterns, and then filling them with petrol or some substance so that, when lit, the ditches would present Martian observers with a "flaming triangle" which would show the existence here of intelligent minds. Even better were the plans of Charles Cross, a French writer of the 1870's, who wanted to build a large mirror to reflect the sun's rays and concentrate them on the surface of Mars, thereby making a vast burning-glass. By swinging the mirror around, Cross explained it would be practicable to write words in the Martian deserts simply by burning the sand. For many years he bombared(轰击) the French government with literature about this plan and was very disappointed when no official interest was shown.
The opinion of the writer is that ______.
A.there may be other intelligent beings in the universe
B.there are other intelligent beings in the universe
C.people living on the earth are almost certainly the only intelligent beings in the universe
D.people living on the earth are definitely the only intelligent beings in the universe
第1题
遥控无人机着陆时,关于大逆风着陆描述正确的是
A.拉平后,速度减小加快,平飘距离缩短
B.拉平后,速度减小加快,平飘距离增长
C.拉平后,速度增大加快,平飘距离缩短
第2题
遥控无人机着陆时,关于大逆风着陆描述正确的是
A.平飘前段,速度较大,飞机下沉较慢,拉杆的动作应快速,防止拉飘
B.平飘前段,速度较大,飞机下沉较慢,拉杆的动作应柔和,防止拉飘
C.平飘前段,速度小,飞机下沉较快,拉杆的动作应快速,防止下沉过快
第5题
遥控无人机着陆到平飘阶段
A.平飘前段,速度较大,下沉较慢,拉杆量应小一些
B.平飘前段,速度较大,下沉较慢,拉杆量应大一些
C.平飘后段,速度较小,下沉较快,拉杆量应适当减小
第7题
遥控无人机着陆时,关于大逆风着陆描述正确的是
A.着陆后,立即刹车
B.着陆后,地速减小快,刹车不要太早
C.着陆后,地速减小慢,刹车不要太晚
为了保护您的账号安全,请在“上学吧”公众号进行验证,点击“官网服务”-“账号验证”后输入验证码“”完成验证,验证成功后方可继续查看答案!