Final answer:
The Defense of Marriage Act (DOMA) is related to the federal issue of marriage and defined marriage as between a man and a woman, but in 2013, a section of DOMA was ruled unconstitutional in United States v. Windsor.
Step-by-step explanation:
The Defense of Marriage Act (DOMA) involves the federal issue of marriage. Enacted in 1996, DOMA defined marriage at the federal level as a union between a man and a woman. While it did not prevent states from recognizing same-sex marriages, it allowed states the option to refuse to recognize same-sex marriages granted in other states. However, in 2013, United States v. Windsor deemed a key section of DOMA unconstitutional, asserting that the federal government could not infringe upon the equal liberty of persons by denying federal benefits and protections to married lesbian and gay couples, which was protected under the Fifth Amendment.
Answer: b) Marriage