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Your sentence
你
Words in this sentence
你
you (informal, as opposed to courteous 您 (nín)); you (Note: In Taiwan, 妳 is used to address females, but in mainland China, it is not commonly used. Instead, 你 is used to address both males and females.)
是
to be (followed by substantives only); correct; right; true; (respectful acknowledgement of a command) very well; (adverb for emphatic assertion)
老师
teacher