A variable-ratio schedule of reinforcement is one in which a response is reinforced only after a(n)

A) specified time period has elapsed.
B) unpredictable time period has elapsed.
C) specified number of responses have been made.
D) unpredictable number of responses have been made.

In a variable-ratio schedule of reinforcement, the reinforcement is given after an unpredictable number of responses have been made. This type of schedule is most effective in maintaining behavior, as it provides a high level of reinforcement while also being unpredictable, which can keep the individual motivated to continue the behavior.