若标准直齿圆柱齿轮模数m＝4mm，齿数z＝22，则其齿顶高为（）
A．5mm
B．4mm
C．6mm
D．3mm
参考答案：B
—I'm afraid I may be a little later.
—_____. [ ]
A. OK. It doesn't matter.
B. I’m sorry to hear that.
C. What's wrong with you?
D. I don't think so.
住宅按照层数，分为低层住宅、多层住宅、中高层住宅和高层住宅，其中中高层住宅为（）层。
A.4～6
B.7～9
C.7～10
D.10层及以上
