In Optimizing Foraging,birds Must Always Balance Which Two Variables

In optimizing foraging,birds must always balance which two variables?

A) Energy taken in per unit time versus the chance of finding a mate
B) Chance of finding a mate versus risk of being eaten by a predator
C) Risk of being eaten by a predator versus the energy density of food
D) Energy taken in per unit time versus risk of being eaten by a predator
E) Chance of finding a mate versus the energy density of food