单项选择题
A．They have no doubts about them. B．They have doubts about them. C．They approve of them. D．They avoid talking about them.
A．Assigning them tasks they have not dealt with before. B．Assigning them tasks which require inventiveness. C．Giving them rewards they really deserve. D．Giving them rewards they anticipat
A．the choice between Spiritual encouragement and monetary rewards B．the amount of monetary rewards for students' creativity C．the study of relationship between actions and their consequences D．the effects of external rewards on students' performance