GMAT Sentence Correction (SC) | Re: Minnesota is the only one of the contiguous forty-eight

In ‘one of the plural + that construction, the ‘that’ is a relative pronoun for the noun before, namely, ‘states’ in this case, which is plural. So ‘that’ is also plural in character and takes the plural verb ‘have’ rather than ‘has’ as erroneously mentioned in A, B and C. Therefore, we can remove those three choices in one sleight
A semicolon connects two Ics that have some relationship. In D, the clauses stand aloof from each other.