Though many replies already exist, here is my 2 cents.
Starfish, blah blah blah, have a strong Z ability, and if <something happens they fix it>, sometimes by the animal overcompensating and growing an extra one or two
C,D,E have a similar problem "overcompensating," is followed by "growing an extra one or two". This is a case of misplaced modifier.
Now A & B remains
(A) one arm is lost it quickly replaces it, sometimes by the animal overcompensating and --> Use of Have in the non-underlined part means we talking about plural star fish.
So B wins!!
Starfish, blah blah blah, have a strong Z ability, and if <something happens they fix it>, sometimes by the animal overcompensating and growing an extra one or two
C,D,E have a similar problem "overcompensating," is followed by "growing an extra one or two". This is a case of misplaced modifier.
Now A & B remains
(A) one arm is lost it quickly replaces it, sometimes by the animal overcompensating and --> Use of Have in the non-underlined part means we talking about plural star fish.
So B wins!!