It's warm in Harbin today．
The thief who was caught stealing on the bus couldn't ______ the fact that the passenger's purse was found in his pocket.
如图所示，在磁铁正上方用弹簧挂着一条形磁铁，开关闭合后，当滑片P从a端向b端滑动过程中，则电流表的示数____ ，弹簧的长度将____ （选填变小、不变或变大）．
