Explain how the 10th amendment supports a states decision to outlaw same-sex marriage.

"The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."

The US has no authority where it is not gifted powers from the constitution. In this amendment gives a fair amount of room, but since it does not explicitly state that the US government has authority over this topic, it is left to the states and its citizens. All the government can do is agree, since it has no jurisdiction over this topic, the state can set laws into place for that state.
Therefore, the Federal government can not restrict them for their decisions, and it is not necessary for the state to change it unless they, or the citizens say it is.

the correct answer is d