单选题 What do scientists say about the collision of an asteroid with Earth?

A、 It is very unlikely but the danger exists.
B、 Such a collision might occur once every 25 years.
C、 Collisions of smaller asteroids with Earth occur more often than expected.
D、 It's still too early to say whether such a collision might occur.

【正确答案】 A

【答案解析】[解析] 本题属细节性问题。这个问题出现在文章的第二段，But there are also thousands whose orbits put them on a collision course with Earth．首先我们细细阅读这一部分，然后对比四个选项。通过对比四个选项，我们发现和原文内容最接近的是A选项It is very unlikely but the danger exists。这个选项是对原文内容的概括和总结：Experts think an asteroid big enough to destroy lots of life might strike Earth once every 500，000 years．Sounds pretty rare—but if one did fall，it would be the end of the world。