A. INTENDING B. SUGGESTING C. MEANING D.REPRESENTINGREAD THE FOLLOWIN...

Câu 35: A. intending B. suggesting C. meaning D.

representing

Read the following passage and mark the letter A, B, C or D on your answer sheet to

indicate the correct answer to each of the questions.

Life in the Universe

Exobiology is the study of life that originates from outside of Earth. As yet, of

course, no such life forms have been found. Exobiologists, however, have done important

work in the theoretical study of where life is most likely to evolve, and what those

extraterrestrial life forms might be like.

What sorts of planets are most likely to develop life? Most scientists agree that a

habitable planet must be terrestrial, or rock-based, with liquid surface water and

biogeochemical cycles that somewhat resemble Earth’s. Water is an important solvent

involved in many biological processes. Biogeochemical cycles are the continuous

movement and transformation of materials in the environment. These cycles include the

circulation of elements and nutrients upon which life and the Earth’s climate depend. Since

(as far as we know) all life is carbon-based, a stable carbon cycle is especially important.

The habitable zone is the region around a star in which planets can develop life.

Assuming the need for liquid surface water, it follows that most stars around the size of our

sun will be able to sustain habitable zones for billions of years. Stars that are larger than the

sun are much hotter and bum out more quickly; life there may not have enough time to

evolve. Stars that are smaller than the sun have different problem. First of all, planets in

their habitable zones will be so close to the star that they will be “tidally locked” – that

is one side of the planet will always face the star in perpetual daylight with the other

side in the perpetual night. Another possible obstacle to life on smaller stars is that they

tend to vary in their luminosity, or brightness, due to flares and “star spots”. The variation

can be large enough to have harmful effects on the ecosystem. Of course, not all stars of the

right size will give rise to life; they also must have terrestrial planets with the right kind of

orbits. Most solar systems have more than one planet, which influence each other’s orbits

with their own gravity. Therefore, in order to have a stable system with no planets flying out

into space, the orbits must be a good distance from one another. Interestingly, the amount of

space needed is roughly the width of a star’s habitable zone. This means that for life to

evolve, the largest possible number of life-supporting planets in any star’s habitable zone is

two.

Finally, not all planets meeting the above conditions will necessarily develop life.

One major threat is large, frequent asteroid and comet impacts, which will wipe out life each

time it tries to evolve. The case of Earth teaches that having large gas giants, such as Saturn

and Jupiter,.in the outer part of the solar system can help keep a planet safe for life. Due to

their strong gravitation, they tend to catch or deflect large objects before they can reach

Earth.