controll is your awser you vary a factor to measure the results
John and Pat's occupation best explains the difference between their skin pigmentation. Since Pat works as a lifeguard, she is more exposed to the sun, which tans her skin. John, on the other hand, works in the theater, where he isn't exposed to sunlight that much, so he is much lighter than his twin, Pat.
Answer: It is D because they get it from soil and the gas
