名词前缺少一个定冠词。

There's a definite ___article missing before the noun.

"A" 和 "an" 是不定冠词的例子。

"A" and "an" are examples of an indefinite ___article.

在英语语法中，冠词常用于单数名词前。

In English grammar, an ___article is often used before a singular noun.