food在什麼時候是可數名詞

例句:

They are at the end of their food supply.

他們的食物儲備已消耗殆盡。 

Within three days they had exhausted their supply of food.

他們在三天之內就把所有糧食吃光了。

His company offers a flexible packaging service for the food industry.

他的公司爲食品工業提供靈活的.`包裝服務

It seems such a waste to throw good food away.

把好的食物扔掉似乎太浪費了。英語可數名詞一般指普通名詞中人或物的個體,能與不定冠詞a,an連用並且能夠計數的名詞,以及部分人或物的總稱,不可數名詞通常是指不能夠計數的人或物。