组合夹具可以分为（）两大类。
A、大型和小型
B、孔系和槽系
C、旋转式和直线式
D、集中型和分散型
参考答案：B
With the development of science, more new technology _____ to the field of IT. [ ]
A. has introduced
B. is being introduced
C. is introduced
D. was introduced
生物的变异与生物的进化，两者关系为变异不定向，进化是定向的。（）
