目前生产的旋转阳极X线管靶面采用的材料为（）
A.钨铜合金
B.镍铁合金
C.铼钨合金
D.镍钨合金
E.镍铼合金
参考答案：C
— Why is the chemical plant closed?
— Because large quantities of waste water ______ into the Yangtze River.
A．has been released
B．is being released
C．was released
D．have been released
炉料及炉气水当量变化的特征？
