引起急性肾衰竭的肾后性原因有（）

A.结石

B.肿瘤

C.脱水

D.前列腺肥大

E.输尿管外肿瘤压迫

During the next ten years we both worked day and night to

_____ the money we had borrowed.

A．pay off

B．pay for

C．pay to

D．pay back