According to Kellerman, the unhappy adults in the world_____.A．are not brighter than other

According to Kellerman, the unhappy adults in the world_____.

A．are not brighter than others

B．don"t have good education

C．are not doing the things they are best at

D．are not duly encouraged in life

请帮忙给出正确答案和分析，谢谢！