What Is the Evolutionary Advantage of Extra-Pair Copulations in Birds

What is the evolutionary advantage of extra-pair copulations in birds?

A) For males,increased reproductive success and for females,the chance to mate with genetically superior individuals.
B) For males,the chance to mate with genetically superior individuals and for females,increased reproductive success.
C) For males,increased reproductive success and for females,the chance to have other females (thought to be the sisters of the mates) assist with the rearing of the offspring.
D) For males,the chance to have other females (thought to be the sisters of the mates) assist with the rearing of the offspring and for females,increased reproductive success.