XJK型浮选机叶轮叶片顶端与盖板内缘之间的间隙常叫做（）。
A.径向间隙
B.轴向间隙
C.无方向间隙
参考答案：B
They are ___________.[ ]
A. talk
B. talking
C. talks
What did the student do _________ Friday morning? [ ]
A. on
B. in
C. /
D. at
