His mother _______ at the age of 90.
A:passed by
B:passed away
C:passed down
D:came to herself
一根旗杆在阳光照射下,在地面上投下一个旗杆的影子.自早晨到黄昏这段时间内,旗杆影子长度变化是 ( )
细胞核是遗传信息库,使细胞____的控制中心.