若要使房子的门窗都朝北,房子只能建在( )
A:本初子午线上
B:北极点上
C:南极点上
D:赤道上
But I am pretty sure about one thing it will probably be the most ____(值得做的).
用显微镜观察根尖纵切面切片:根尖由根冠、____、____、成熟区四部分组成.