作玉米、谷粒讲时,有复数,+s；作谷物讲时没有复数,是不可数名词.

corn

n.(小麦等)谷物;谷粒;(尤指脚趾上的)钉胼，鸡眼

复数： corns

The field had been ploughed and planted with corn.

这块地已犁过并种上了玉米。

I know for a fact that baby corn is very expensive in Europe

我知道玉米笋在欧洲的确价格不菲。

Aid workers helped distribute corn, milk and other staples.

救助人员协助分发谷物、牛奶及其他必需的食物。