From an Evolutionary Perspective, What Role Does Extramarital Sex Play

From an evolutionary perspective, what role does extramarital sex play in the survival of our species?

A) The more partners men have, the more children they are likely to father.
B) The more wives men have, the stronger are marital bonds.
C) The more partners men have, the more stable does family life become.
D) The more wives men have, the lower is their sperm count.