Harrison sends an e-mail to his boss. harrison expects a response within five minutes, but he can’t himself and checks every 30 seconds. after five minutes, a replying e-mail is delivered just as he expected. which of the following statements is true? a. harrison is on a fixed-interval schedule of reinforcement. b. harrison is on a variable-interval schedule of reinforcement. c. harrison is on a fixed-ratio schedule of reinforcement. d. harrison is on a variable-ratio schedule of reinforcement.