I       use a clock to wake me up because at six o'clock each morning the train comesby my house.         [ ]

 A. couldn't          

B. mustn't          

C. shouldn't        

D. needn't

某物质被肾小球自由滤过后，又全部被肾小管重吸收，其血浆清除率

A．等于零

B．小于肾小球滤过率

C．等于肾小球滤过率

D．大于肾小球滤过率