设计电路板文件的扩展名是（）。
A.Sch
B.ERC
C.PCB
D.DDB
参考答案：C
As you can see, the number of cars on our roads _____ rising these days. [ ]
A. was keeping
B. keep
C. keeps
D. were keeping
以下病变属于结核的是（）
A.痰核
B.流火
C. * * 结核
D.瘰疬
E.流痰
