Katy's Fences pays its employees based on the number of feet of fence they put up (called "fence feet"). Josey, a female, and Kevin, a male, are Katys employees with comparable jobs. Because Kevin can carry heavier loads of raw materials (wood slats and hardware) and therefore can assemble fence faster and ultimately builds more "fence feet" than Josey during a work day, Kevin is paid more than Josey . This is

a. not illegal discrimination.

b. gender discrimination.

c. reverse discrimination.

d. disparate-impact discrimination.