21. 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
选项C为何不可? 思路:主语:CELLS, 谓语三个动词并列:adhere....., beat.., and adopt....
原本只有adopt specialized orientations exclusive of one another 是跟adhere to one another 相左,E选项even though they beat in unison and adopt则是说连beat in unison也是adhere相左,与原意不符,仅做参考,再请NN指导!