People who exercise _____ are less likely to feel stress. [ ]

A. regularly

B. formally

C. mostly

D. publicly

形成条件反射的重要条件是

A．大脑皮质必须健全

B．要有非条件刺激强化

C．要有适当的无关刺激

D．非条件刺激出现在无关刺激之前

E．无关刺激与非条件刺激在时间上多次结合