A:﹣ 17 +5
B:﹣ 17 +4
C:﹣ 17 ﹣3
D:17 ﹣4
下列各项中,属于特异性免疫的是
He lost his bag. Luckily there isn't anything ____ (value) in it.
如图是电磁继电器的构造和工作电路示意图,要使它的电磁铁对衔铁的吸引力大些,以下做法可行的是( )