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An SC doubt.

by gmat_perfect » Wed Mar 16, 2011 8:28 am
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

I can explain D, C, and E:

In both C and D it seems that days erupted, so they are out.

"Having erupted" in E, does not have an agent to be modified; therefore, E is out.

We are between A and B.

I am torn between these two.

I know "sporadically erupting" modifies the clause before COMMA, but I am unable to explain exactly why B is wrong.

Thanks.
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by Geva@EconomistGMAT » Wed Mar 16, 2011 8:39 am
The issue with B is one of tense. The past perfect is used to denote an action of state that began before another action in the past, and was completed by the time the later action or state happened/occurred.
"by the time the police arrived, the thieves had alrady fled the scene" --> indicates that the thieves had fled before the police even got there.
When you say "lava had been an underground remnant", you are implying that it stopped being a remnant the moment it erupted, which is wrong: lava is always a remnant of the earth's earliest days, and the fact that it erupted does not make it less so.
gmat_perfect wrote: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

I can explain D, C, and E:

In both C and D it seems that days erupted, so they are out.

"Having erupted" in E, does not have an agent to be modified; therefore, E is out.

We are between A and B.

I am torn between these two.

I know "sporadically erupting" modifies the clause before COMMA, but I am unable to explain exactly why B is wrong.

Thanks.
Geva
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by GMATMadeEasy » Wed Mar 16, 2011 10:06 am
I know 'which' is sometimes a bit debatable but in C because of prepositional phrase , which refers to 'an underground remnant' not Earth's earliest days . There is a question in OG in which OG clearly mentions what which refers to . (translation of Iliad , which ...)
C.was an underground remnant of Earth's earliest days, which sporadically erupted
C should be wrong because intention is lava was erupting not "underground remnant " . Need clarification on this please. Whereas in A, it clearly refers to the subject 'lava' .
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