A:树的年轮
B:太阳
C:流星
D:指南针
在“共点力合成”实验中,
如图用带电体接触它的金属球,就有一部分电荷转移到两金属箔片上,两箔片就张开,则两箔片上带的是____(填“同种”或“异种”)电荷.
The farmer is very busy because he's so _______ sheep to keep and so ______ work to do every day.