A、Water. B、Distance. C、Atmosphere. D、Surface temperature. C演讲中提到，“从我们自己的太阳系，我们了解到一颗行星的大气层对于它的气候和供养生命的潜能是至关重要的。”故选C。

I am in search of another planet in the universe where life exists. [23-1] I can’t see this planet with my naked eyes or even with the most powerful telescopes we currently possess. But I know that it’s there. And understanding contradictions that occur in nature will help us find it.
    On our planet, where there’s water, there’s life. So we look for planets that orbit at just the right distance from their stars. At this distance, shown in blue on this diagram for stars of different temperatures, planets could be warm enough for water to flow on their surfaces as lakes and oceans where life might reside. [23 - 2] Some astronomers focus their time and energy on finding planets at these distances from their stars. What I do picks up where their job ends. I model the possible climates of exoplanets. And here’s why that’s important: there are many factors besides distance from its star that control whether a planet can support life.
    Take the planet Venus. It’s named after the Roman goddess of love and beauty, because of its benign, ethereal appearance in the sky. But spacecraft measurements revealed a different story. The surface temperature is close to 900 degrees Fahrenheit, 500 Celsius. That’s hot enough to melt lead. Its thick atmosphere, not its distance from the sun, is the reason. It causes a greenhouse effect on steroids, trapping heat from the sun and scorching the planet’s surface. The reality totally contradicted initial perceptions of this planet. [24] From these lessons from our own solar system, we’ve learned that a planet’s atmosphere is crucial to its climate and potential to host life.
    We don’t know what the atmospheres of these planets are like because the planets are so small and dim compared to their stars and so far away from us. For example, one of the closest planets that could support surface water—it’s called Gliese 667 Cc—such a glamorous name, right, nice phone number for a name—it’s 23 light years away. So that’s more than 100 trillion miles. Trying to measure the atmospheric composition of an exoplanet passing in front of its host star is hard. It’s like trying to see a fruit fly passing in front of a car’s headlight. OK, now imagine that car is 100 trillion miles away, and you want to know the precise color of that fly.
    So I use computer models to calculate the kind of atmosphere a planet would need to have a suitable climate for water and life.
Here’s an artist’s concept of [25] the planet Kepler-62f, with the Earth for reference. It’s 1,200 light years away, and just 40 percent larger than Earth. Our NSF-funded work found that it could be warm enough for open water from many types of atmospheres and orientations of its orbit. So I’d like future telescopes to follow up on this planet to look for signs of life.
23. Different from other astronomers, what does the speaker do?
24. What is crucial to a planet’s climate and potential to host life?
25. How far away is the planet Kepler-62f from earth?