What is the finding of the Canadian researchers? ( )(本题2.5分)

A、 Encouraging positive thinking may do more harm than good.
B、 The power of positive thinking is limited.
C、 Unhappy people cannot think positively.
D、 There can be no simple therapy for psychological problems.
出自:西安石油大学-石油工程技术-大学英语l(下)