--Was his father very strict with him when he was at school?---Yes.He had never praised him ___ he became one of the top students in his grade.

A．after

B．unless

C．until

D．when

通常将本金安全的、具有高度流动性的资产称为无风险资产。下列不能完全视为无风险资产的是( )。

A．(A) 短期回购

B．(B) 央行票据

C．(C) 货币市场基金

D．(D) 现金