Reading Comprehension
试题详情
文章：
| Line | In addition to conventional galaxies, the universe |
| contains very dim galaxies that until recently went | |
| unnoticed by astronomers. Possibly as numerous | |
| as conventional galaxies, these galaxies have the | |
| (5) | same general shape and even the same |
| approximate number of stars as a common type of | |
| conventional galaxy, the spiral, but tend to be much | |
| larger. Because these galaxies’ mass is spread out | |
| over larger areas, they have far fewer stars per unit | |
| (10) | volume than do conventional galaxies. Apparently |
| these low-surface-brightness galaxies, as they are | |
| called, take much longer than conventional galaxies | |
| to condense their primordial gas and convert it to | |
| stars—that is, they evolve much more slowly. | |
| (15) | These galaxies may constitute an answer to the |
| long-standing puzzle of the missing baryonic mass | |
| in the universe. Baryons—subatomic particles that | |
| are generally protons or neutrons—are the source | |
| of stellar, and therefore galactic, luminosity, and so | |
| (20) | their numbers can be estimated based on how |
| luminous galaxies are. However, the amount of | |
| helium in the universe, as measured by | |
| spectroscopy, suggests that there are far more | |
| baryons in the universe than estimates based on | |
| (25) | galactic luminosity indicate. Astronomers have long |
| speculated that the missing baryonic mass might | |
| eventually be discovered in intergalactic space or as | |
| some large population of galaxies that are | |
| difficult to detect. |
题目：
It can be inferred from the passage that which of the following is an accurate physical description of typical low-surface-brightness galaxies?
选项:
A、
They are large spiral galaxies containing fewer stars than conventional galaxies.
B、
They are compact but very dim spiral galaxies.
C、
They are diffuse spiral galaxies that occupy a large volume of space.
D、
They are small, young spiral galaxies that contain a high proportion of primordial gas.
E、
They are large, dense spirals with low luminosity.
答案:
C
提问：
想问一下老师，这里的these low-surface-brightness galaxies是不是指前面的dim galaxies。然后A选项可以解释一下为什么不选吗？是因为per unit volume吗？谢谢！
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