A:地壳的上部
B:地球内部的外核
C:上地幔上部的软流层
D:岩石圈中部
联想形状写声母
①____ ② ____ ③____
The teacher often asks us _______ English as _______ as possible.
已知点(x,y)满足x+y≥1x-y≥-12x-y≤2,目标函数z=ax+2y仅在点(1,0)处取得最小值,则a的范围为( )