Final answer:
Sean is being paid with a variable ratio schedule of reinforcement. Option A
Step-by-step explanation:
The schedule of reinforcement that Sean is being paid with is variable ratio (A). In a variable ratio schedule, the number of responses needed for a reward varies. This is the most powerful partial reinforcement schedule and is commonly used in situations where a high response rate is desired, such as sales commissions.
Sean's salary depends on how many shoes he can sell, so the number of shoes sold varies and therefore fits the variable ratio schedule. Option A