My old neighbour Charles felt ________ after his children moved out.
A:lonely
B:safely
C:angrily
D:happily
如图所示,用磁铁的N极在钢棒AB上从A端向B端反复摩擦几次后,钢棒就具有了磁性,这种现象称为____,且钢棒的A端为____极.
如图是尿液形成示意图,请据图回答: