We Observe a Remarkable Increase in Brain Size in the Order

We observe a remarkable increase in brain size in the order primates.What is this associated with?

A) Primates have long growth and development periods to accommodate the development of complex behaviors in individuals.
B) Primates have shorter developmental periods to accommodate the necessary energy expenditures of larger brain size.
C) Primate brain size is determined primarily by genetic drift and has no clear adaptive role,other than in humans.
D) The relatively large brain in primates is due to the expansion of the olfactory system during primate evolution.