Hey guys can somebody explain what the concept of comma before "aND" means?I was unable to do two questions in a row and both had a similar concept:

Neanderthals had a vocal tract that resembled those of the apes and so were probably without language, a shortcoming that may explain why they were supplanted by our own species.

(A) Neanderthals had a vocal tract that resembled those of the apes
(B) Neanderthals had a vocal tract resembling an ape's
(C) The vocal tracts of Neanderthals resembled an ape's
(D) The Neanderthal's vocal tracts resembled the apes'
(E) The vocal tracts of the Neanderthals resembled those of the apes

look at the sentence later part.
AND so were without a language.
were : plural subject.
no comma before AND.
subject of first clause before end is the subject of clause after and.
so straight option C,D and E are out.

............

Nuclear fusion is the force that powers the Sun, the stars, and hydrogen bombs, merging the nuclei of atoms and not splitting them apart, as in nuclear reactors.

(A) merging the nuclei of atoms and not splitting them apart, as in nuclear reactors
(B) merging the nuclei of atoms instead of splitting them apart, like nuclear reactors
(C) merging the nuclei of atoms rather than splitting them apart, as nuclear reactors do
(D) and merges the nuclei of atoms but does not split them apart, as is done in nclear reactors
(E) and merges the nuclei of atoms, unlike atomic reactors that split them apart

the comma after 'bombs' strongly suggests the coming of an adverbial modifier (as in choice c).