Jake and Kourtney have the same job classification, but Jake is paid at a higher rate. Which situation below would justify such a decision?

Jake and Kourtney have the same job classification, but Jake is paid at a higher rate. Which situation below would justify such a decision? Jake works the night shift, and night hours are less desirable for most workers. Jake is a U.S, citizen; therefore his pay should be higher than that of non-Americans. Kourtney is pregnant; therefore her productivity is assumed to be lower. Jake is physically disabled; therefore he should be paid more than Lisa