— Yes, they are my plants.
A:grandfather
B:grandfather's
C:grandfathers
— What do you do on Sundays?— I often ____ .
假设从空中N点看到地表的同一半球的两条纬线a.b(纬度a>b),M点为N点在地表的垂直投影。若此时M点为夜半球的正中心,且一年中纬度最高,则( )
原始大气中不含有下列哪种气体?( )