learning how to repair motors takes a long time
learning how to repair motors takes a long time,__1,don't they 2,does it 3,do they 4,doesn't it 四个中选哪个呢？为什么？谢谢。
4 是对的 这句的主语是learning how to repair motors 是分词短语 是单数的 所以用IT 这句是肯定句 所以用DOESN‘T
答：选B 反意疑问句的附加问句中的助动词（连系动词或者情态动词）应该和主句一致。主句中如有情态动词或Be动词，反意疑问句中相应也应该用情态动词或Be动词。主句中若是...详情>>
答：I haven't window molding catalogs on hand. catalogs 产品目录 haven't ~ something ~ o...详情>>
问：working hard vs. hard working
答：there are no defferent.详情>>
