She had just finished her homework ______ her mother asked her to practise playing the piano yesterday.

A．when

B．while

C．after

D．since

去年，和羊毛的批发价不同，棉花的批发价大幅度下跌。因此，虽然目前商店中棉织品的零售价还没下跌，但它肯定会下跌。以下哪项如果为真，最能削弱上述论证？（）

A.去年由于引进新的工艺，棉织品的生产加工成本普遍上升

B.去年，羊毛批发价的上涨幅度，小于棉花批发价的下跌幅度

C.棉织品比羊毛制品更受消费者的欢迎

D.零售价的变动一般都滞后于批发价的变动