Geologists once thought that the molten rock known as lava was an underground remnant of Earth's earliest days, sporadically erupting through volcanoes, but they now know that it is continuously created by the heat of the radioactivity deep inside the planet.

A: was an underground remnant of Earth's earliest days, sporadically erupting

B: had been an underground remnant of Earth's earliest days and sporadically erupted

C: was an underground remnant of Earth's earliest days, which sporadically erupted

D: would be an underground remnant of Earth's earliest days that sporadically erupted

E: was an underground remnant of Earth's earliest days, having sporadically erupted


OA is given as A.

Isn't 'sporadically erupting' modifying 'earliest days' in A? Can you please explain?

jrankoth,

relative pronouns such as which (answer choice C) refer to the noun or noun phrase immediately preceding the pronoun (days in choice C). However, "-ing" verb forms are more "free" to describe their logical referents. In choice A, it is logically clear that erupting refers to the molten rock known as lava. Thus, sporadically erupting is a grammatically correct construction in choice A.

To clarify this concept I have included two brief examples below.

I studied my GMAT material all day on Saturday, which resulted in a major improvement on the actual test.

Incorrect: This sentence indicates that Saturday resulted in a major improvement on the actual test.

I studied my GMAT material all day on Saturday, resulting in a major improvement on the actual test.

Correct: This sentence indicates that my studying resulted in a major improvement on the actual test.

Hope that helps!
-dan

Thanks a lot Dan; that's very helpful.

Please remember to cite the source; if you don't, we'll have to delete the question.

what is "having sporadically erupted" in choice d modifying?

why is A preferable?

This is a ManhattanGMAT question.

In D, the "that" indicates a noun modifier and must modify the closest preceding primary noun. In this case, it would modify "remnant" as the closest primary noun. (Not days - days is part of a prepositional phrase attached to and directly describing remnant, so the prepositional phrase is just a descriptor and doesn't function as the primary noun.)

A is preferred because it is the only one without grammatical errors. Among other reasons:
B incorrectly uses the past perfect "had been"
C incorrectly uses "which" to indicate a noun modifier, requiring it to modify the closest preceding primary noun, which is not lava (what it should refer to)
D as described above (and also uses incorrect tense "would be")
E "having erupted" implies that lava no longer erupts from volcanoes; this is untrue and, even if you didn't know that, this contradicts the meaning in the original sentence, which indicates that the lava does still erupt - always follow the meaning of the original sentence unless there is something logically impossible about the meaning