You are watching a rat pressing a lever in a skinner box to obtain food pellets. the rat is pressing the lever at a slow, steady rate, but it does not stop, even when a food pellet is delivered. in this example, the reinforcement schedule that is in place is most likely:
a. a variable-ratio schedule.
b. a fixed-interval schedule.
c. a variable-interval schedule.
d. a fixed-ratio schedule.

d.a fixed-ratio schedule.                

Explanation:

Fixed-ratio schedule: In psychology, the term fixed-ratio schedule is being used in operant conditioning and is defined as a reinforcement schedule in which a particular response is being reinforced after a specific number of responses.

Example: A cat will be given food only after a fixed number of a particular response or behavior i.e if the cat will 'meow' three times then the cat will be given food.

In the question above, the statement signifies a fixed-ratio schedule of reinforcement.