昨天他们在图书馆学习。

They were studying in the library yesterday.

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They were studying in the library yesterday.

were 是 be 动词的过去式复数形式,在这里与 studying 一起构成过去进行时,表示过去某个时间正在进行的动作。

在 App 中完整学习这张卡片

在 App 中学习