构成地壳的最基本物质是（）。
A、土壤
B、矿物
C、晶体
D、颗粒
参考答案：B
若方程组 3x+y=k+1x+3y=3
(2012·重庆高考)—________ you interrupt now? Can't you see I'm on the phone?
—Sorry Sir, but it's urgent.
A．Can
B．Should
C．Must
D．Would
