Kelli always tries to be very helpful because she believes it increases her chances of receiving help at a future time. Kelli's thinking most closely reflects the concept of

What is another name for the method of successive approximations?

a) shaping b) extinction c) punishment d) negative reinforcement

Which characterizes the most typical customer of prostitutes?

A) Low-class single men B) Middle-class single men C) Middle-class married men D) Low-class married men