滚压螺纹时，工件的外圆尺寸应车到螺纹中径尺寸。( )
参考答案：对
______ pollution control measures are expensive, many industries hesitate to adopt them.
A．Although
B．However
C．Because
D．On account of
《空气环境质量标准》依据使用目的和保护目标将其划分为（）。
A.三级
B.Ⅳ类
C.二级
D.Ⅴ类
