．Ram explained to his mother ________ he would get home late that night because of extra work.

A．that

B．which

C．what

D．whether

以依法可以转让的股票出质的，质权自( )起成立。

A．质押合同订立 B．交付股票
C．向证券登记机构办理出质登记
D．公司同意之日