TPO15閱讀 第2篇 Mass Extinction 第10題 - 英檢

One interesting test of the Alvarez hypothesis is based on the presence of
the rare-earth element iridium (Ir). Earth’s crust contains very little of
this element, but most asteroids contain a lot more. Debris thrown into the
atmosphere by an asteroid collision would presumably contain large amounts of
iridium, and atmospheric currents would carry this material all over the globe.
A search of sedimentary deposits that span the boundary between the Cretaceous
and Tertiary periods shows that there is a dramatic increase in the abundance
of iridium briefly and precisely at this boundary. This iridium anomaly offers
strong support for the Alvarez hypothesis even though" no asteroid itself has
ever been recovered."

10. In stating that" no asteroid itself has ever been recovered," the author
emphasizes which of the following?

A. The importance of the indirect evidence for a large asteroid
B. The fact that no evidence supports the asteroid-impact hypothesis

想請問一下這兩個答案有什麼不同呢?

我是選B 可是答案是A 實在想不出為什麼
還請高手幫忙解惑 謝謝 :)
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