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 : a

I marked B.

My Reasoning :
There are two actions of the past in the sentence.

Geologists once thought ....... lava was an underground

Hence I thought of employing the past perfect tense.


Please help.
I am having problems identifying the correct places where perfect tenses are actually required.

The reason that past perfect is not required here is that the two past events are not at different points in time. Geologists thought that the lava they observed was a remnant of an earlier time. Since the geologists' thoughts and the lava existed simultaneously, there is no need for a complex tense.

Correct: "I used to think that chocolate was only for dessert, but now I eat it with every meal."

"What we found in the cave was a surprise to all of us."

We use past perfect when the past event precedes some other past event that we have specified:

"I had been running every day until I broke my ankle."

"Prior to the publication of Mr. Singh's paper, scientists had thought that lava was a remnant of earth's earliest days."

"When we explored the cave, we found that someone else had visited it before us."

_________________
Dmitry Farber
Manhattan GMAT Instructor