在英语中，'a' 和 'an' 被称为不定冠词。

In English, 'a' and 'an' are called ___indefinite ___articles.

不定冠词用于指代非特定的名词。

An ___indefinite ___article is used to refer to a non-specific noun.

学习语法时，理解不定冠词对 B1 水平的学生很重要。

When learning grammar, understanding the ___indefinite ___article is important for B1 students.