On the first trial, a rat in a Skinner box is reinforced for the first bar press it makes after 50 seconds have elapsed. On the second trial, the first bar press after 70 seconds is reinforced. Although it varies from trial to trial, the average works out to one reinforcer every 60 seconds. The rat is on a schedule of reinforcement. fixed-ratio fixed-interval variable-interval variable-ratio

variable-interval.                      

Explanation:

Variable-interval schedule: In psychology, the term "variable-interval schedule" is a schedule of reinforcement that falls under the operant conditioning theory which was determined by B. F. Skinner.

In the variable-interval schedule, reinforcement is being given to a specific response only after a specified amount of time has been elapsed or passed i.e, an unpredictable time yet this amount of time is associated with a variable or changing schedule.

In the question above, the given statement represents the variable-interval schedule of reinforcement.

answer; the region experienced a surplus of food;