在通电螺线管中插入下列物体后使其磁性一定增强的是( )
A:铜棒
B:铅棒
C:铝棒
D:铁棒
①NaOH ②AgNO3 ③Na2CO3 ④NaBr ⑤FeCl2.
在分层设色地形图中,绿色一般表示( )
Busy as he is, he still comes by and picks me up at his c ____ .