The Fact That People from Some Cultures Lack an Enzyme

The fact that people from some cultures lack an enzyme that allows them to digest milk reflects the fact that

A) cultural practices can affect human evolution.
B) cultural practices are shaped by the local geography.
C) people from different cultures differ more in terms of their genes than they do in terms of their cultural practices.
D) this inability is due to a proximal cause.
E) genetic differences are difficult to overcome.