A:took place
B:have taken place
C:were taken place
D:have been taken place
已知:x+y=2,xy=7,求x3y+xy3的值.
一____were you when I was in town?
—In a village.
如图所示,矩形线圈放置在水平薄木板上,有两块相同的蹄形磁铁,四个磁极之间的距离相等,当两块磁铁匀速向右通过线圈时,线圈仍静止不动,那么线圈受到木板的摩擦力方向是( )