Scientists have recently found evidence that black holes—regions of space in which matter is so concentrated and the pull of gravity so powerful that nothing, not even light, can emerge from them—probably exist at the core of nearly all galaxies and the mass of each black hole is proportional to its host galaxy.
(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. The question can be accessed at GMAT Club)
The sentence says that scientists have recently found evidence for two things.
- The black holes probably exist at the core of nearly all galaxies
- The mass of each black hole is proportional to its host galaxy
Please note that the sentence also provides a lot of information about black holes within two dashes. You can read the idea between the dashes. However, the more important thing is that when you start reading after the closing dash, read as if the dashes and everything contained within the dashes weren’t there. In other words, you shouldn’t get lost in the deluge of information in the dashes and should be able to connect the part of the sentence that appears after the dashes to the part before the dashes.
There are two problems with this sentence:
- “That” is missing after ‘and’. To make it clear that the evidence suggests “that the mass of each…”, we need to place ‘that’ before “the mass of each…”. Without ‘that’, it may seem like another independent clause having nothing to do with evidence.
- The second problem is with the meaning. It doesn’t make sense to say that the mass of X is proportional to a galaxy. Probably, we mean to say that the mass of X is proportional to the mass of a galaxy. Therefore, the second part of the sentence should be modified to say “proportional to the mass of its host galaxy”. Please note that when we are evaluating the options, we need to be flexible i.e. even though it seems to be “proportional to the mass of its host galaxy”, it may eventually turn out to be “proportional to the size of its host galaxy”.
(A) Incorrect. For the two errors pointed above.
(B) Correct. Both the errors have been corrected in this sentence. ‘that’ in “that of its host galaxy” refers to “the mass”.
(C) Incorrect. It repeats the second error “proportion to its host galaxy” of option A.
(D) Incorrect. Singular verb “exists” doesn’t go with plural subject “black holes”.
(E) Incorrect. For the following reasons:
- Singular verb “exists” doesn’t go with plural subject “black holes”.
- ‘That’ is missing after “and”.