单项选择题 3) “People who live along this road receive their mail in these boxes.”   “Why are all of the____ ?” A、mailboxes painted gray  B、mailboxes that painted gray C、gray painted mailboxes   D、mailboxes painted as gray

单项选择题 对于埋地管道，防腐的方法是（）。 A、涂刷、喷涂防腐涂料 B、设置绝缘防腐层

单项选择题 斜二轴测图轴向伸缩系数是（ ）