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【单选题】

A "small" comet impact on Earth is the most likely extraterrestrial (地球外的) object to kill millions of people and it could happen at any moment, according to a British expert.
Dr. Matt Genge, from London’s Natural History Museum, has investigated the damage that a wide range of small meteorites (陨星) and comets would have, if they struck our planet. He identifies comets between just 50 and 100 meters wide as the most terrifying destructive, with massive heat and shock waves burning people and crushing buildings. He explains that while meteorites bigger than two kilometers could wipe out humanity, these hits are expected only once every million years or so. Smaller ones could still lead to the deaths of tens of millions and arrive much more frequently. These are therefore much more erous, he said. A 60-meter-wide comet exploded over Siberia in 1908 with 600 times the energy of the bomb dropped on Hiroshima. It laid waste to a 40-kilometer-wide patch of forest, but, fortunately, the area was unpopulated. Comets of this size are expected to strike the Earth every 100 to 300 years.
If the 1908 comet had arrived just eight hours later, it would have struck London, killing everyone and destroying everything as Dr. Genge described.
Dr. Genge looked at the physical properties of meteorites and comets to identify the Siberian-type strike as the most erous. Ironically, it is because the 50to 100-meter-wide comets are so weak that they are so erous. They break up into fragments which explode just a few kilometers above the ground--"the optimum (最优) altitude for maximum devastation (毁灭)," said Dr. Genge. Stone and metal meteorites of similar size are much stronger and do not break up and explode. However, 100-meter-wide metal meteorites would create a blast area of 60 kilometers across compared to just two kilometers for a stone meteorite of the same size. The metal’s higher density is to blame.
Dr. Genge believes that this type of ysis will help to decide what level of er an Earth-bound object would pose and aid decisions about what course of action to take.
The author cited the 1908 comet as an example for the purpose of______

A.
explaining why "small comets" are the most terrifying
B.
predicting when a comet would strike Earth
C.
showing how frequently a comet visits Earth
D.
illustrating the massive energy released by "small comets\
题目标签:地球陨星
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【单选题】文明的人类对地球不具有的能力是( )。

A.
改造能力
B.
改变能力
C.
保护能力
D.
破坏能力

【单选题】关于地球的环境人口容量的说法正确的是(  )

A.
现今世界上人口太多,已大大超过了地球的环境人口容量
B.
未来世界的人口,不会达到地球环境人口容量的极限值
C.
将全球人口稳定在110亿或略多一些,可使地球上的人维持合理健康的生活
D.
目前的科技水平不能解决人口过多带来的问题,人口的进一步增长,后果不堪设想

【多选题】人类对地球的影响包括

A.
生物进化
B.
物质循环
C.
地质沉积
D.
水循环

【单选题】关于地球的说法,正确的是[ ]

A.
经线虽长短不一,但都是闭合的圆圈
B.
地轴是竖直的
C.
南极点是所有纬线在地球南端的交点
D.
本初子午线就是0°经线