电气火灾事故的常见原因包括( )。
A．设备缺陷、安装不当
B．电气设备过热
C．电火花、电弧
D．电气设备操作不当
参考答案：A,B,C
已知命题p：|m+1|≤2成立．命题q：方程x2-2mx+1=0有实数根．若￢P为假命题，p∧q为假命题，求实数m的取值范围．
Sometimes the expert ________ a task from a historical point of view.
A．doesn’t need to approach
B．dare settle
C．needs not to solve
D．dare not to deal with
