化简a3·a2的结果是[ ]
A.a
B.a5
C.a6
D.a9
答案:B
A poet and artist going to speak tomorrow afternoon to us about Chinese literature.
A.is
B.are
C.was
D.were
通常将雷电引起的电力系统过电压,称()
A.外部过电压
B.感应雷过电压
C.直击雷过电压
D.操作过电压