In Sexual Selection, Why Do Males Often Compete for Female

In sexual selection, why do males often compete for female reproductive resources?

A) Because males often have extravagant displays such as dancing and plumage
B) Because males are more physically capable of acts of physical contest
C) Because female reproductive structures are invaginated
D) Because spermatozoa are motile
E) Because oocytes tend to be fewer in number than spermatocytes