That vs. Who
The general rule is: a person is a who; a thing is a that. You would say: Is this the chair that has a broken leg? and Is he the man who has a broken leg? An anonymous animal is a that but an animal with a name is a who. For example: Was it Fifi who bit the mailman? but Was it a stray dog that bit the mailman?
It has now become acceptable to use that when referring to a person. However, using who often helps the understanding of a sentence that contains both a person and a thing. It makes it easier to understand to whom (or to which) you are referring.
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