一般可数名词前如果没有其他限定词如his, this, those等修饰的时候,要么用a,要么加s。因为可数名词要么表示单数,要么表示复数。如 你的例句应该为:i like roast ducks. 再如:People usually have three meals every day.The boy under the tree is Mike. The boys under the tree are playing games.This pen is mine.而不可数名词名词前一般不加冠词。如:Air has colour or taste.详细请访问