861
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
(E) they must know how to pace themselves

[spoiler]OA-C
IMO-E[/spoiler]

why is E wrong?