下列材料中属于软磁材料的是（）。
A.硅钢
B.稀土钴系材料
C.铵铁硼
D.电工纯铁
参考答案：A, D
世界上最大的河流是
A．亚马孙河
B．尼罗河
C．长江
D．密西西比河
Mary bought three pairs of sports shoes the other day, but ______ is expensive. [ ]
A. none of which
B. neither of which
C. none of them
D. neither of them
