You'd better ask a ______, such as your aunt or sister, to look after your children while you are away.
A：classmate
B：neighbor
C：relative
在奥斯特实验中我们发现：在直导线周围放上小磁针，当导线中通电时，小磁针转动．这说明 ____，电流通过它产生的 ____对磁体施加力的作用，当电流方向改变时， ____方向改变．
about with of at in
