Why Is the Ability to Digest Lactose in Adults Most

Why is the ability to digest lactose in adults most prevalent in Northern Europe, North America, and Australia?

A) Today, most of the world's dairy farming goes on in these locations.
B) The populations in these locations consume the most dairy products.
C) Populations in temperate climates are more likely to adapt to use dairy products.
D) Many of the people in populations in these areas are descendants of hunter-gatherers.
E) Many of the people in these areas are descendants of the first dairy farmers in human history.