食物蛋白质生物学价值是指
A.氮吸收量/氮摄入量B.氮摄人量/氮吸收量C.氮储留量/氮吸收量D.氮吸收量/氮储留量E.氮储留量/氮摄入量
参考答案:C
They must be visiting the Great Wall of China, _____? [ ]
A. mustn't they
B. must they
C. aren't they
D. are they
擦试耙料机时是否能用水?为什么?