疑惑

fishleungyaoUID: 3309646

阅读36套第十三套中的第四题有个疑问Which of the following, if true, would cast most
doubt on Phinney's estimate of the probability of
Earth rocks hitting Mars?
○A Rather than going in random directions, about
25 percent of all particles ejected from Earth
go in the same direction into space.
○B Approximately 100 meteorites large enough to
make a noticeable crater hit the Earth each year.
○C No rocks of Earth origin have been detected
on Mars.
○D The velocity of rocks escaping from Earth's gravity is
lower than the velocity of meteorites hitting the Earth.
○E No craters more than 60 miles across have
been found on Mars.



全文是：According to astronomer S.A. Phinney, kicking a rock hard enough to free it from Earth's gravity would require a meteorite capable of ** a crater more than 60 miles across. Moreover, even if Earth rocks were freed by meteorite impact, Mars's orbit is much larger than Earth's, so Phinney estimates that the probability of these rocks hitting Mars is about one-tenth as great as that of Mars's rocks hitting Earth. To demonstrate this estimate, Phinney used a computer to calculate where 1,000 hypothetical particles would go if ejected from Earth in random directions. He found that 17 of the 1,000 particles would hit Mars.

我选的是C，错在哪里搞懂了，17/1000 的概率本来就有肯能没有击中的，所以C并不能很好的质疑。我的疑惑在于，选项A中，random并不排除有相同方向的吧，如：我们从五个班里不分男女性别，随机挑出五个人并不排除五个全是男生/女生的情况，或者类似的，这并不能说明就不是random了。同样的，选项中25%的相同方向，另外75%没有说明，可能是各个方向，也可能是有部分重复了25%的方向，但并不能说明这就不是random了吧？就是说random并不排除一致性的存在啊。真心求教！谢谢

苏梳眠UID: 2717864

75%不能涵盖其他各个方向吧，100%才能涵盖各个方向吧~
其他几个选项和题目不太相关吧。

fishleungyaoUID: 3309646

2# 苏梳眠 还是有点迷糊……难道我钻牛角尖了……好吧～如果考试时遇到了，就果断排除法了……ps：谢谢苏版主啊！