In Orr v. Orr, on what basis did the U.S. Supreme Court hold that Alabama's alimony law was unconstitutional?

A.  The alimony law was not available to a wife if she had been unfaithful and therefore violated the wife's right to equal protection.

B.  The alimony law presumed that the husband was wealthier than his wife and therefore subjected him to cruel and unusual punishment.

C.  The alimony law was arbitrary and unfair because it required the wife to establish financial need.

D.  The alimony law made alimony available only to wives and therefore violated the husband's right to equal protection.