用配方法将方程x²+6x-11=0变形为（　　）

A．（x-3）²=20

B．（x+3）²=20

C．（x+3）²=2

D．（x-3）²=2

According to Skinner, a well-known behaviorist psychologist, ______, was much more effective than ______ in a teaching situation.

A. reward...reasoning


B. reward...punishment
C. reasoning...reward


D. reasoning...punishment