闭合开关,小磁针静止时的位置如图所示,请你标出电源的正负极。
阀芯是调节阀的关键部件,形式多种多样,但一般分为两大类,即直行程阀芯和()。
A、球形阀芯
B、平板刑阀芯
C、角行程阀芯
D、套筒形阀芯
Happily, the victories of our team came from the Asian Games in Guangzhou __________.
A.one by one
B.one after another
C.little by little
D.one another