In which situation can a same-sex couple file as married filing jointly?

A same-sex couple can file as married filing jointly if they are legally married in any jurisdiction, regardless of whether their home jurisdiction recognizes same-sex marriage. This means that if a couple is legally married in one of the states or countries that recognizes same-sex marriage, they are afforded the same federal tax benefits as opposite-sex couples, including the option to file their taxes jointly.

In the specific case of choice D, the couple is in a same-sex marriage but resides in a jurisdiction that does not recognize same-sex marriage. Since their marriage is legally valid in another jurisdiction where it was performed, they can still file jointly for tax purposes at the federal level. This reflects the legal standing that once a couple is married, they maintain that marital status irrespective of the laws of their current place of residence.

In contrast, the other options involve relationships that are not recognized as marriages under federal law, such as domestic partnerships and civil unions, which do not grant the same tax benefits or filing status rights as a legally recognized marriage. Therefore, those couples are not eligible to file jointly.