A:15°
B:20°
C:30°
D:60°
下图为甲、乙两个国家人口出生率和死亡率统计图。读图,回答问题。
乙国的人口增长模式为( )
______ Mary ______ John has been to China before, but they know a lot about it.
到南极科学考察的最佳时间是( )
甲、乙两小车运动s﹣t图象如图所示,由图象可知( )