Mr Li is one of the businessmen who _____ very rich. [ ]
A. is
B. are
C. was
D. were
答案:B
立式车床由于工件及工作台的重力由机床()或推力轴承承担,大大减轻了立柱及主轴轴承的负载,因而能长期保证机床精度。
A、主轴
B、导轨
C、夹具
D、附件
白云鄂博矿冶炼的特殊性是指()。
A.含K+、Na+、F-高
B.品位低
C.含稀土坑素
D.含S高