She was completely absorbed in her book and missed her stop on the train.

was 是 be 动词的过去式，表示"是"或"处于某种状态"。 absorbed 是动词 absorb 的过去分词形式，absorb 本意是"吸收"，引申为"全神贯注"。在这里表示"被吸引、沉浸"的状态。 in 是介词，表示"在...之中"，这里表示"沉浸于某种状态或活动中"。 was absorbed in 是一个固定搭配，表示"全神贯注于..."或"沉浸于..."。