____是少年健康的大敌。
In April, the weather in some places in Shanxi was really changeable. People still remember they have _______ four seasons in a week.
读西气东输线路图, 西气东输线路不经过( )
读下图，此图显示我国古代经济重心的南移经历了一个漫长的过程，与图中第③处对应的时期是（ ）
① ② ③
