A:说明书中偏硅酸的化学式书写不规范,其正确的化学式为H2SiO3
B:说明书中的“钙”是元素
C:偏硅酸中硅元素(Si)的化合价为+4价
D:纯净优质的矿泉水属于纯净物
People in Colombia needn't make plans to meet their friends. They often just drop by them.
如图示意图我国经济重心的南移经历了一个漫长的过程,与图中的①相对应的时期应该是( )