Paul and Michael sell magazine subscriptions by telephone. Paul is paid $1.00 for every five calls he makes, while Michael is paid $1.00 for every subscription he sells,
regardless of the number of calls he makes. Paul's telephoning is reinforced on a
____ schedule, whereas Michael's is reinforced on a _____ schedule.
A) variable-ratio; fixed-ratio
B) fixed-ratio; variable-ratio
C) fixed-ratio; variable-interval
D) fixed-interval; variable-ratio