LS高频显示相位角大报警的原因有（）。
A、纵封板位置不对
B、纸管扭转严重
C、高频有故障
参考答案：A, B, C
什么是煤的灰分？什么是煤的矿物质？两者之间有什么联系和区别？
Contract closeout is a process that involves（）
A.Customer satisfaction analysis and final payment
B.Administrative closeout and archiving records
C.Finial contractor payment and Lessons learned
D.Product verification and administrative closeout
