Faye works as an administrator and receptionist for Garage Door Store. The store withholds federal taxes from Faye's pay, and controls the methods and details of the performance of her work. Faye is not authorized to modify the prices or other terms of a sale at the store. Homer installs Garage Door products at the buyers' locations. ​Refer to Fact Pattern 19-2. Garage Door authorizes Homer to sell garage door upgrades and accessories at the buyers' locations at prices that Homer negotiates with those buyers. With respect to sales at those locations, Homer is Select one:

a. ​an employee only.
b. ​a principal.
c. ​an employee and agent.
d. ​an independent contractor.