光学经纬仪按精度可以分为5个等级,即DJ07、DJ1、DJ2、DJ5、DJ15。( )
参考答案:错
Rita is _____ baby. She is very lovely. [ ]
A. eight-month-old
B. an eight-month-old
C. eight months old
D. an eight month old
A.若磁场正在增强,则电场能正在减少,电容器上极板带正电
B.若磁场正在减弱,则电场能正在增强,电容器上极板带正电
C.振荡电流的变化周期为:2π
D.电场能量的变化周期为:π