How Does Gene-Culture Co-Evolution Explain Lactase Persistence in Some Adult

How does gene-culture co-evolution explain lactase persistence in some adult populations in the world?

A) It was an advantage to be lactose tolerant to consume cheese.
B) Milk which was drunk in times of famine caused a mutation in the lactase gene.
C) Adults who were able to consume milk survived better in famines and so had a selective advantage.
D) Over time some populations developed bacteria in the gut that consume lactose.