英语 热门试卷

阅读下列短文，从短文后每题所给的A、B、C和D四个选项中，选出最佳选项，并在答题卡上将该项涂黑。

A

Questioning the existence of aliens is something that scientists have done for decades. In fact, most people do believe that aliens exist in some fashion. The main necessities for life are water and some form of energy source. Not surprisingly, there are some planets, exoplanets and moons that fit the bill. Here are several best chances at finding life in the universe.

◆TRAPPIST-1

TRAPPIST-1 is a planetary system a few dozen light-years away, whose discovery was announced in early 2017. This system consists of seven Earth-like exoplanets orbiting an "ultra-cool" star, and it is one of our shots at finding possible life beyond our own solar system.

◆Titan

Titan is the largest moon of Saturn, the sixth planet from our Sun. This moon could potentially harbor life but possibly not in the sense that we think. Titan does not exactly fit the description of being in a typical habitable zone.

Titan has water, and it has liquid. It just doesn't have liquid water. The water on this moon is completely solid because of the extremely cold temperature.

◆Europa

Europa is one of Jupiter's moons here in our own solar system. It is another candidate due to its potential to hold liquid water. Europa is thought to have all the necessities for life including water, energy sources, and the right chemical build-up.

◆Mars

The Red Planet, the fourth from the Sun, is probably one of the most talked-about potential candidates for extraterrestrial(地球外的) life and even for human colonization. Despite some different voices, finding extraterrestrial life on Mars really is a serious possibility.

We know by now that we won't find little green men or any intelligent form of life that we understand. However, there is evidence that there was and may still be microscopic life on the small red planet.