问题详情

Research has shown that _________.
A．Dropouts are substantially below Ph.D"s in financial attainment
B．the incentive factor is a minor one in regard to pursuing Ph. D. studies
C．The Ph. D. candidate is likely to change his field of specialization if he drops outD. about one-third of those who start Ph.D
D．work do not complete the work to earn the degree请帮忙给出正确答案和分析，谢谢！