—Was it by cutting down staff      are not diligent enough       she saved the firm?

—No, it was by improving work efficiency．

A．that; when

B．that; what

C．who; how

D．who; that

从理论上讲，如果利率水平一直不变，债权人在债券期满之前将债券转让获得的差价就是其持有债券这段时间的利息收益转化形式。（）