对于用电势源静止励磁机的系统，其励磁顶值电压倍数应按发电机端正序电压为额定值的（）计算。
A.0.9
B.0.8
C.0.7
D.0.6
参考答案：B
The futility of the program resulted from poor planning.
A．possible failure in the future
B．ineffectiveness and uselessness
C．blindness to its mistakes
D．potential disaster
设u=f(x2+y2，xz)，z=z(x，y)由ey+ey=ez确定，其中f二阶连续可偏导，求
