又是TPO15 的阅读 没良心的答案

sunshine12358

TPO 15 阅读MASS　EXTINCTIONS
14.Therehave been many attempts to explain the causes of mass extinctions.

Answer Choices

○Asteroid impacts,evolutionary developments, and changes in Earth's climate and in the positionsof the continents have all been proposed as possible causes of massextinctions.
○Researchers have observed26-million-year cycles in extinction rates of a number of fossil groups thatcould all be attributed to the same cause.      
○According to the Alvarezhypothesis, much of the iridium originally present on Earth was thrown into theatmosphere as a result of an asteroid impact that also caused a massextinction.              
○The unusual distribution ofiridium on Earth and the presence of craters and heat-shocked quartz arecentral to the theory that an asteroid impact caused the late Cretaceous event.
○The collision between Earthand a large asteroid resulted in massive damage and generated enough heat tocause irreversible changes in Earth's atmosphere.                
○There was a particularlylarge mass extinction that occurred around 250 million years ago at the end ofthe Permian period, whose cause could not be determined.
我给出的答案，1、4、6。原答案给的2能对吗？文中第三段明确说了“
Each mass extinction may have had a differentcause.”

另外一个是有争议的第十题：
Paragraph6: One interesting test of the Alvarez hypothesis is based on the presence ofthe rare-earth element iridium (Ir). Earth’s crust contains very little of thiselement, but most asteroids contain a lot more. Debris thrown into theatmosphere by an asteroid collision would presumably contain large amounts ofiridium, and atmospheric currents would carry this material all over the globe.A search of sedimentary deposits that span the boundary between the Cretaceousand Tertiary periods shows that there is a dramatic increase in the abundanceof iridium briefly and precisely at this boundary. This iridium anomaly offersstrong 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?      
○Theimportance of the indirect evidence for a large asteroid
○Thefact that no evidence supports the asteroid?impact hypothesis

○Thereason many researchers reject the Alvarez hypothesis
○Theresponsibility of scientists for not making the effort to discover the asteroiditself
我选的C，是这样考虑的。文中最后一句的减半据说Iridium支持了Alvarez的观点，后半句说即使是在有没实物证据记录的条件下。逻辑关系是：Iridium支持Alvarez，no recorded不支持Alvarez。显然选C。答案给的A是个毛意思啊~~

thedayathome

也纠结这个题。。。

karlaxu

强调的是“在地球发现Ir的事情”，这件事情就是Indirect evidence, 所以说就算no asteroid itself has ever been recovered, 也能support 行星碰撞地球的Alvarez hypothesis