thephoenix 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

intrested to understand the error in E

My understanding is as follows

E changes the meaning of the original sentence......E states emphatically that the eruption process is over unlike in the original sentence..infact, this problem exists with all answer choices, except A .

The ing form in A helps the modifier to modify the entire clause unlike a modifier such as who, which, etc.
that would have modified only the preceding noun "days" in this case

I think this is a bad question because the meaning (after choosing a) is still unclear., whether the modifier modifies molten rock known as lava or underground remnant of Earth's earliest days......however i am clear that A is the right answer.