Dairy Products Are Generally Nutritious but Most Human Adults Cannot

Dairy products are generally nutritious but most human adults cannot digest them. This is because

A) They generally stopped drinking milk when they were toddlers.
B) Milk sugar is called lactase and most adults have the genetic disease "lactase-intolerance."
C) Most adult human stomachs have a different chemical composition than children's stomachs.
D) Most adult humans don't produce lactase, the enzyme necessary to digest the dairy sugar lactose.
E) Most adult humans simply don't have access to dairy products and gradually lose the ability to digest them.