老师不得不反复强调这个语法规则，因为学生们总是忘记。

The teacher had to iterate the grammar rule repeatedly because the students kept forgetting it.

iterate 是动词，来自拉丁语 iterare（重复），意思是"重复说或做"。这个词强调为了确保理解或记忆而进行的重复行为。