In 1974 a large area of the surface of Mercury was photographed from varying distances, which revealed a degree of cratering similar to that of the Moon’s.


(A) which revealed a degree of cratering similar to that of the Moon’s

(B) to reveal a degree of cratering similar to the Moon

(C) revealing a degree of cratering similar to that of the Moon

(D) and revealed cratering similar in degree to the Moon

(E) that revealed cratering similar in degree to that of the Moon
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Not getting why option B is incorrect

this is really a modifier and comparison question.

Without question, A, B and D can be eliminated because the comparison is not equal. There must be 'that of' that refers back to surface.

Between C and E is much more difficult.
'revealing' is a participial modifier which modifies the entire noun phrase.
'That' is a relative clause that modifies the subject 'area',

therefore the answer choice is C.

Please let me know if I am wrong about the modifier as I may not be entirely correct.

First, the term "appositive" here does not indicate the commonly accepted meaning: a noun modifying a noun. Some grammarians use the term "appositive relative clause" to indicate what we generally call "non-essential modifiers". (But in GMAT the jargon does not matter.)

Now coming to your query:
This is very odd indeed. This may be one of the rare occasions in which one OG explanation contradicts another. The relative pronoun "which" does not have a noun to refer to - the second part should modify the entire clause and a present participle modifier "revealing..." is correct.

I would seek further advice from the expert of the experts mikemcgarry .

Another problem is that a modifier starting with "that" will be a noun modifier, and must therefore modify the preceding noun. The distances themselves didn't reveal the cratering. C correctly uses an adverbial modifier (", revealing . . . ") to indicate that this revelation is a result of the entire preceding clause.
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karant, the modifier does need to make sense in relation to the preceding clause, but it doesn't need to refer to a person who performed the action. It just explains the result of the action. A large area was photographed, and this revealed the cratering. It doesn't matter who took the photograph. It was probably automated, anyway.
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A. Can be knocked off - Incorrect placement of the Relative Pronoun, ‘which’- Pronoun error. INCORRECT
B. The Pronoun error is rectified in this option. However, it can be knocked off because ‘the degree of cratering is incorrectly compared to the moon. Incorrect- Comparison Error. INCORRECT.
C. Correct usage of the adverbial modifier, ‘revealing’. It correctly refers to the action, ‘was photographed……’ the action revealed a degree of cratering. Correct comparison- cratering similar to that of the moon’ (Correct Answer)-
D. Wrong Comparison… Cratering is compared to ‘Moon”- ( Comparison Error)-INCORRECT
E. ‘That’ appears to modify distances- error similar to that in Option A..INCORRECT
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I have a simple explanation.
If you look at the original sentence and concentrate on its meaning--- It says Nothing about the 'purpose' of the 'Photograph' being taken.
The Result just happened simultaneously
Whereas For B-- The Result of 'finding the similarity in craters' is because of deliberately 'Photographing' the landscape.


In short B changes the meaning of A drastically, although it is a grammatically correct sentence.

cubs, there is a difference in meaning, although here it's not crucial. The difference is in what is revealed: cratering or the degree of cratering. Did we learn that cratering exists, or did we learn how much cratering there is? I could imagine going with the usage in E even if the craters were already known, but "revealing a degree" shows more clearly that what we discovered was how much cratering there is.
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I understand why C is correct, but I didn't understand why A was incorrect so I selected A initially. Then I read the OG and I now understand that the reason C is correct is the same reason A is incorrect.

(A) "which revealed a degree of cratering similar to that of the Moon\('s\)"

The comma + which modifier is correctly used.
However we have a redundancy error caused by the conflict between the relative pronoun "that" and possessive "Moon's".

Substitution will make this easier to see:
, "which revealed a degree of cratering similar to that (cratering) of the Moon's (cratering)" - it's hard to see without substitution, but it's logical to conclude (A) is redundant.

(C) "revealing a degree of cratering similar to that of the Moon"

This is correct and here are the rules you need to understand to see this :
Verb-ing modifier:
- If separated by comma, modifies preceding clause and associates with the subject
- If separated by comma, modifies the following clause or modifies only the subject
- If not separated by comma, modifies the noun

That is a relative pronoun that has a number of rules but here are the ones relevant to this:
- Relative pronouns must be placed close to the noun they modify otherwise it will be incorrect:
- substitute the antecedent for the relative pronoun to confirm agreement and meaning