绝缘接头是指电缆（）在电气上断开。
A.仅金属护套
B.仅金属护套、接地屏蔽
C.金属护套、接地屏蔽和绝缘屏蔽
参考答案：C
The old lady had one son and two daughters, _____ treated her well, _____ made her very sad. [ ]
A. none of whom; which
B. neither of them; which
C. none of them; it
D. no one of whom; as
当来流速度为亚音速时，喷管或扩压管的断面形状为（）。
A.收缩形扩压管
B.扩张形喷管
C.缩放形扩压管
D.缩放形喷管
