Thosewhoentermarathonssoonlearnthat,tosucceedinthesegruelingcompetitiveevents,runnersmustbeinexcellentcondition,haveunshakableself-confidence,and,mostimportantofall,knowhowtopaceyourself.（）
(A)knowhowtopaceyourself
(B)isknowinghowtopaceyourself
(C)knowhowtopacethemselves
(D)youmustpaceyourself
(E)theymustknowhowtopacethemselves