Circulatory system

[GmatKiss]

A peculiar feature of the embryonic mammalian circulatory system is that in the area of the heart the cells adhere to one another, beating in unison and adopting specialized orientations exclusive of one another.
(A) beating in unison and adopting
(B) they beat in unison while adopting
(C) beat in unison, and adopt
(D) beating in unison yet adopting
(E) even though they beat in unison and adopt

OA after some discussion

[aspirant2011]

A peculiar feature of the embryonic mammalian circulatory system is that in the area of the heart the cells adhere to one another, beating in unison and adopting specialized orientations exclusive of one another.
(A) beating in unison and adopting ---- we need a transition word
(B) they beat in unison while adopting ---- not parallel
(C) beat in unison, and adopt --- same as A
(D) beating in unison yet adopting --- ing verb modifies the subject cells of the previous clause and uses a contrasting word yet
(E) even though they beat in unison and adopt ---- same as A

OA after some discussion

[avik.ch]

I will go for D.

as there should be a participle pharase which have to modify - "A peculiar feature of the embryonic mammalian circulatory system is that in the area of the heart the cells adhere to one another"

A and D goes for that.

But in A - "and" is not proper here because as far as meaning is concerned both the actions are contradictory in nature.
So I will go for D.

What is the OA ?

[VivianKerr]

IMO: D

It comes down to meaning. The heart-cells "adhere" and "beat in unison" which shows they are similar BUT then they also "adopt...orientations EXCLUSIVE of one another." These are contrasting concepts, so we'd need a transition word here to express that.

D preserves the parallelism but provides us with that transition word.