牙折常发生于下述何种牙位（）。
A.上前牙
B.下前牙
C.单尖牙
D.前磨牙
E.磨牙
参考答案：A
运行的变压器轻瓦斯动作发出信号，收集到的为淡灰色强烈臭味可燃气体，由此可以判断变压器发生的为纸和纸板故障
What happened to the Nuclear Family in the middle of the twentieth century
A．It changed greatly.
B．It was criticized.
C．It remained a normal structure.
D．It was lost.
