YJ27滤嘴接装机错位鼓轮的作用是将原来在一个轮槽中的三段滤嘴段错开排列在（）个前后不同的槽位。
A.1
B.2
C.3
D.4
参考答案：C
Professor Zhang handed out the textbooks to all the students, except _____ who had already taken them. [ ]
A. these
B. ones
C. the ones
D. the others
某材料的表观密度为1 400 kg/m3，密度为1 600kg/m3，其孔隙率为( )。
A．12.5%B．87.5%C．11.5%D．14.28%
