People That Are Lactose Intolerant Have a Functional Copy of the Lactase

Multiple Choice

People that are lactose intolerant have a functional copy of the lactase gene but are unable to digest lactose. Which statement must be TRUE about lactose-intolerant people?

A) They have the same lactase gene as lactose-tolerant people.
B) They produce a lactase enzyme but it does not fold properly.
C) They have a lactase gene made of RNA instead of DNA.
D) They produce a lactase enzyme that digests glucose instead of lactose.