In ancient Hindu law, which one of the following is not an approved form of marriage?

In classical Hindu law, the Smritis recognised eight forms of marriage: four approved (prasasta) forms—Brahma, Daiva, Arsha, and Prajapatya—and four unapproved (aprasasta) forms—Asura, Gandharva, Rakshasa, and Paishacha. Accordingly, Brahma, Daiva, and Prajapatya are approved forms of marriage, whereas Asura (where the bridegroom gives wealth to the bride's kinsmen and the bride) is an unapproved form of marriage.