—Why are the two students standing at the gate of the teachers'office?

—They________to each other in class and________.[ ]

A. have whispered; are punishing

B. had whispered; were punished

C. whispered; are being punished

D. are whispering; were being punished

原始投资额不同，特别是项目计算期不同的多方案比较决策，最适合采用的评价方法是 ( )。

A．获利指数法

B．内部收益率法

C．差额投资内部收益率法

D．年等额净回收额法