beating vs beat

[vivekcall81]

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
can anybody explain why C is wrong.

[RonPurewal]

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
can anybody explain why C is wrong.

in this sentence, all three of choices (a), (c), and (d) are grammatically correct. however, (d) is the only one of those three that actually makes sense in the context of the sentence.

specifically:
the point here is that you must notice the CONTRAST between "beating in unison" (i.e., an activity that the cells perform together) and "adopting specialized orientations exclusive of one another" (i.e., an activity that the cells perform separately, and, in fact, in a mutually exclusive fashion).

therefore, for this sentence to make sense, it must use a transition word that actually suggests contrast.
"and" doesn't suggest contrast; if you have a list of items connected with "and", then the items in the list should be similar to, or should reinforce, each other.
"yet" suggests contrast.

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here's a much more pedestrian example of the same thing:

she practiced for months, and she still couldn't perform the maneuver gracefully --> doesn't make sense

she practiced for months, but she still couldn't perform the maneuver gracefully --> makes sense

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this problem should serve as a nice wake-up call to those posters who seem to believe that SC problems can be addressed as entirely mechanical entities. make sure that you pay attention to the meaning of the sentence!