单项选择题
A.80% B.75% C.30% D.72%
A.80 B.-200 C.-240 D.-180
A.磁铁矿-赤铁矿-褐铁矿 B.赤铁矿-磁铁矿-褐铁矿 C.褐铁矿-磁铁矿-赤铁矿 D.磁铁矿-褐铁矿-赤铁矿