托福考试

根据网考网考试中心的统计分析，以下试题在2019/5/6日托福考试习题练习中，答错率较高，为：73%
【单选题】
{$mediaurl} What aspect of the K-T extinction event does the professor mainly discuss
A、The scientists who first discovered it.
B、A、phenomenon that could have caused it.
C、Its similarities with prior extinction events.
D、Its long-term effects on the planet.
网考网参考答案：B，答错率：73%
网考网试题解析：
[解析] 6-11 [Professor (female)] Class, let’s jump right into the lecture for today. Q7 Let me start by telling you an interesting fact that’s relevant to the rest of the lecture: the energy released by the impact of a large asteroid on our planet is equivalent to several million nuclear weapons. Tell me, why is this information important--from a historical perspective [Student A (male)] Well, if an impact like that can release as much energy as--as millions of nuclear weapons...well,Q7 that’s catastrophic enough to explain extinction events in Earth’s history. [Professor] Exactly. Now by "extinction events" we’re referring to periods in the planet’s history when there’s a very...a very marked decrease in the number of species. Um, and it happens within a relatively short period of time--at least on a geological timescale. There’ve been a handful of extinction events during the past 540 million years, but--but the one that’s, um, generated the most interest--because it killed the dinosaurs--um, it’s the most recent one, the K-T extinction event...which happened 65 million years ago. [Student B (female)] Q8 [Professor], what does "K-T" mean [Professor] Oh, "K-T." Well, "K" is a standard abbreviation for the Cretaceous Period. And "T" is the standard abbreviation for the Tertiary Period. Does anyone want to take a guess, then, about the meaning of the name "K-T" [Student A] Does it mean the extinction event occurred, um, during the Cretaceous and Tertiary Periods [Professor] Sort of. Of course, we aren’t exactly sure how long the K-T extinction event lasted.’Could’ve been a few years...could’ve been a few thousand years...or could’ve been even longer. But for a general figure, we date the K-T extinction event to around the end of the Cretaceous Period and the beginning of the Tertiary Period. It’s basically seen as the dividing line between the two. And Q6 what we’re going to talk about today is the reason why this extinction event happened. Which goes back to what I mentioned earlier--asteroid impacts can be extremely destructive. Uh, before I go on, Q11 I just want to emphasize that no one knows what caused the K-T extinction event...and there’re many hypotheses. The asteroid hypothesis is of course just one of many. Could’ve been volcanic activity, climate change, or sea-level changes...just to name a few theories. But, anyway, let’s get back to the asteroid hypothesis. OK. Now even before there was any, um, evidence for an asteroid impact causing mass extinctions, um, people were talking about the possibility. In 1980, though, we got our first glimpse of evidence that really backed the idea of an asteroid causing-- causing the K-T extinction event. A group of researchers led by Luis Alverez discovered an interesting, um, stripe...uh, in the sedimentary layers of Earth’s crust that date back to the end of the Cretaceous Period and the beginning of the Tertiary Period. At the boundary of these two, um, layers--we call it the K-T boundary--there were deposits of a very rare element: iridium. Alverez and his team discovered that, um, the stripe of iridium was global...it appeared at the K-T boundary in sedimentary layers all over the world. Alverez and his team 查看试题解析出处>>