磁轨制动是接通励磁电流将制动电磁铁吸附在钢轨上与柜面（）产生制动力
A.吸引
B.摩擦
C.排斥
参考答案：A
I am very grateful to my high school teachers, without ________ help I wouldn't be so excellent. [ ]
A. whom
B. them
C. which
D. whose
