Final answer:
If DRA refers to the Defense of Marriage Act, then the correct answer to when the U.S. Supreme Court ruled the Defense of Marriage Act unconstitutional is C. 2013.
Step-by-step explanation:
The statement 'The DRA was implemented on this date' refers to the implementation date of a specific regulatory act or decision, which is not explicitly mentioned in the information provided. However, given the context of the options, it seems that the question could pertain to a well-known governmental act or a historical decision. The provided information about the final rule signed on October 1, 2015, and effective December 28, 2015, refers to an unrelated standard, which does not align with any of the answer choices given.
On the other hand, if the acronym 'DRA' refers to the 'Defense of Marriage Act' (DOMA) mentioned in relation to the U.S. Supreme Court ruling, then the correct answer to when the U.S. Supreme Court ruled the Defense of Marriage Act unconstitutional is C. 2013. This was a significant event in the history of the United States, as it marked a turning point in the recognition of same-sex marriage at the federal level.