一般仪表管线的电伴热采用电热带，而露天安装的仪表箱电伴热却采用的是（）。
A.电热管
B.电热带
C.加热炉
D.电磁棒
参考答案：A
Never before _____ so highly successful in his attempts to change the weather slightly on a very small scale. [ ]
A. man has been
B. man is
C. will man be
D. has man been
牙科电焊机的熔焊原理是（）。
A.电阻热熔焊
B.高频振荡熔焊
C.红外加热熔焊
D.化学熔焊
E.高温熔焊
