在管材中属于非金属管的是（）。
A.无缝钢管
B.铝管
C.塑料管
D.渗铝管材
参考答案：C
Iraq has _____ too many wars since 1990, making his people _____ a lot. [ ]
A. got through; pay
B. looked through; face
C. gone through; suffer
D. passed through; destroy
水轮发电机最近发展起来的制动技术是（）。
A.电制动
B.机械制动
C.风闸制动
D.多次制动
