That's or thats? (grammar help please!)?

Hi! So I'm writing a paper and I'm saying, "Darfur is a region of western Sudan thats government is..." My question is about the "that"-- should it be "that's" (even though that means "that is") or "thats" (with no apostrophe)? My computer says it should be "that's", but I need a serious, concrete answer for the... show more Hi! So I'm writing a paper and I'm saying, "Darfur is a region of western Sudan thats government is..." My question is about the "that"-- should it be "that's" (even though that means "that is") or "thats" (with no apostrophe)? My computer says it should be "that's", but I need a serious, concrete answer for the correct grammar. Thank you!
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