Up to Tuesday's attack, the worst school shooting in the U. S. was in March 1998 in Jonesboro,______two boys, aged 11 and 13, shot and killed a teacher and four girls.

A．while

B．where

C．when

D．then

某投资项目的财务内部收益率为20%。当建设投资增加10%时，内部收益率变为18%，基准收益率为12%，由此得出敏感性系数为（）。

A．-2

B．-1.53

C．-1.43

D．-1