. _______ one time, Manchester was the home of the most productive cotton mills in the world.
A、On
B、By
C、At
D、Of
【正确答案】：C
【题目解析】：C【句意】曾经，曼彻斯特是世界上几个大棉厂的诞生地。【解析】at one time意为“曾经，一度”。如：At one time the little girl formed the habit of visiting Einstein after school every day。有一段时间，那个小女孩养成了个习惯，每天放学后都去看望爱因斯坦。选项A，B和D都不能和one time构成短语，故只有C正确。