[原创] 大全861题应该选哪个？

1.        Those who enter marathons soon learn that, to succeed in these grueling competitive events, runners must be in excellent condition, have unshakable self-confidence, and, most important of all, know how to pace yourself.

(A) know how to pace yourself

(B) is knowing how to pace yourself

(C) know how to pace themselves

(D) you must pace yourself（C）

(E) they must know how to pace themselves

参考答案给的C，不过如果选C的话，为什么and前面要加逗号破坏了谓语动词的平行，使得原句子更象一个由and连词组成的并列句，使得更像选E而不是C。大家觉得呢？

这个平行结构是这样：must be...., (must) have...., and (must)know... 没有疑问呀