1. What do the speakers mainly discuss?
a. Whether life could exist outside a star’s habitable zone
b. Techniques used by researchers to detect exoplanets
c. Exoplanets that share certain characteristics with Earth
d. Characteristics of several recently discovered red dwarf stars
解析：(从第1分37秒开始，原文重现：OK, good. An Earth-like planet.
Now, as to that, there are some recently detected exoplanets that might actually be Earth-like.)
2. What does the professor say about the host star Gliese 581?
Click on 2 answers.
a. It is larger than the Sun.
b. It is cooler than the Sun.
c. It is a relatively young star.
d. It is relatively close to Earth.
解析：(从第2分钟开始，原文重现：This host star is considered a near neighbor of our solar system because it's only about 20 light years away. It's pretty close by astronomical standards. And being a red dwarf star, it's small and relatively cool, at least compared with the Sun.)
3.What does the professor suggest about life on other planets?
a. It most likely does not exist.
b. It probably will not be discovered in the near future.
c. It probably would not be similar to life on Earth.
d. It could possibly be found even on gas giants.
破题关键词汇：life on other planets
解析：(从第1分01秒开始，原文重现：First, as for discovering life. Well, I think that sort of discovery is pretty far in the future, but it is an eventual goal.)
4. What did researchers discover about the planet Gliese 581 d when they reexamined it?
a. It is made entirely of rocks.
b. It is not able to support an ocean.
c. It is smaller than previously thought.
d. It is closer to its host star than previousty thought.
破题关键词汇：Gliese 581 d, reexamined
解析：(从第2分54秒开始，原文重现：And when its orbit was originally calculated it was thought to be too far away from its host star to be warm enough to support a liquid ocean, let alone carbon-based life. But then its orbit was recalculated and now we see that Gliese 581 d is within its host's habitable zone.)
根据原文可知，最初计算时，Gliese 581 d的轨道被认为距离其主恒星太远了，但是后来再次计算其轨道时，发现Gliese 581 d已经在其主恒星的宜居带中了，所以它比之前想象的距其主恒星的距离要近，所以D选项正确。
5. Why is the planet Gliese 581 e unlikely to support carbon-based life?
a. It is too hot.
b. It is too small.
c. It is covered in ice.
d. It is made entirely of gas.
破题关键词汇：Gliese 581 e, unlikely
解析：(从第4分04秒开始，原文重现：meaning it's very close to the star, and therefore too hot for water, for an ocean)
根据原文可知，Gliese 581 e距离其主恒星太近了，所以温度很高，所以A选项正确。
6. What does the professor find most exciting about the discovery of the planet Gliese 581 e?
a. It showed that some exoplanets have an atmosphere like Earth’s.
b. It helped researchers better understand exoplanets’ orbits.
c. It showed that the technology exists to detect small exoplanets.
d. It proved that some stars’ habitable zones are larger than once thought.
破题关键词汇：most exciting, Gliese 581 e
解析：(从第4分09秒开始，原文重现：However, the fact that it's relatively close to the size of Earth, small, in astronomical terms, that was pretty exciting. It's impressive that we have the technology to detect it and it bodes well for future research.)
根据原文可知，非常impressive的是现有的科技已经能探测到如此小的行星如Gliese 581 e，所以C选项正确。