What Is the Fitness Benefit of Polygamy in Birds That

What is the fitness benefit of polygamy in birds that rear precocious young?

A) Females will copulate with many males to ensure that all of their eggs are fertilized.
B) Females don't have to decide on one mate, and can copulate with as many males as each female deems worthy to share her genes with in reproduction.
C) Fit males don't have to help feed and rear young and can spend this time seeking and mating with many females.
D) Females don't have to spend time rearing young and can mate and rear additional broods during a breeding season.
E) Both males and females spend little time with courtship and brood-rearing, and don't tax their own physiology so they can breed again in subsequent breeding seasons.