At the beginning of class, the noise of desks____________ could be heard outside the

classroom.                    [ ]

A．opened and closed

B. to be opened and closed

C. being opened and closed

D．to open and close

承运人对货物的灭失或者损坏的赔偿限额，按照货物件数或者货物毛重计算时，（）。

A.以二者中赔偿限额较低的为准

B.以二者中赔偿限额较高的为准

C.取二者均值

D.在二者中任选