镗轴的回转精度主要决定于镗轴主轴套前，后轴承内外滚道的圆度、同轴度误差、主轴套同轴承的装配精度和主轴套与镗轴的配合精度。
参考答案：对
Traffic conditions in Beijing _____ for decades. At first people only complained about jams during rush hours,
but today every hour is rush hour. [ ]
A. is worsening
B. have worsened
C. have been worsening
D. worsened
暖季型草坪中，（）耐阴性最弱。
A.狗牙根
B.马尼拉
C.结缕草
D.天鹅绒
