우유

In a sentence

• 나는 아침에 우유를 마십니다.

  I drink milk in the morning.

  Here, '우유' is used as the direct object of the action '마시다' (to drink), signified by the object particle '를'.

• 우유가 없다면 커피를 마실 수 없습니다.

  If there is no milk, I cannot drink coffee.

  In this instance, '우유가' functions as the subject of the verb clause, indicated by the subject particle '가'.

• 우유 한 잔을 주시겠어요?

  Could you give me a glass of milk?

  Here, '우유' is being quantified with '한 잔' (a glass), and used as the object of the verb '주다' (to give).