数字式万用表的显示部分通常采用()
A.液晶显示器
B.发光管显示
C.荧光显示
D.光敏二极管
参考答案:A
—Can you tell me __________the book?
—Last year.
A.when did you buy
B.when do you buy
C.when you buy
D.when you bought
两平行金属板水平放置,板间距为0.6cm,两板接上6×103V电压,板间有一个带电液滴质量为4.8×10-10 g,处于静止状态,则油滴上有元电荷数目是(g取10m/s2)( )
A.3×106
B.30
C.10
D.3×104