—Oh. Mary's not here these days. Is she ill? —_____.Her mother told me that she was in hospital.
A:I am afraid so
B:I hope not
C:I don't mind
D:I don't think so
如图所示,是“探究导体在磁场中运动时产生感应电流的条件”实验装置.铜棒ab、电流表、开关组成闭合电路.