A:ought to joi
B:should have joined
C:would rather not have joined
D:would like to have joined
中国人开始使用铁农具是在( )
把下列词语补充完整。
战死____ 鼓声____
甲、乙两名滑冰运动员,M甲=60kg,M乙=40kg,面对面拉着弹簧测力计做圆周运动进行滑冰表演,如图所示.两人相距0.8m,弹簧测力计的示数为9.2N,下列判断中正确的是( )
为了促进骨骼的发育,除了给儿童多补充含钙、磷多的食物,还应补充( )