此句中的studying是分词形式。be doing sth 是表示进行时 am/is/are doing是现在进行时,表示正在进行的动作。was/were doing 是过去进行时,表示过去的某个时间正在进行的动作。e.g. i'm reading. 我现在正在看书。i was reading when you called me. 你电话我的那个时候,我正在看书。明白了吗?
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