18. 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

不可以。

v1, v2, but v3。有歧义，因为不知道v3倒底和哪个转折。