A:in
B:at
C:on
我的年龄是爸爸的____
我的年龄是爷爷的____.
如图为12月22日甲乙丙丁四个城市昼夜长短示意图(阴影部分表示黑夜).读图完成下题.
________all the work finished ahead of time,I feel relaxed and very happy to be reading the papers.
如图所示,通电螺丝管旁放有一枚小磁针,根据已画出的磁感线完成作图:
(1)标出小磁针静止时的N极;
(2)标出电源“+”、“﹣”极.