State governments are not sub-units of the federal government, but instead each is and does not report in any constitutional way to the federal government. a. a confederacy c. dependent b. sovereign d. an oligarchy

We are looking here for something that is compatible with "does not report in any constitutional way to the federal government" - and the correct answer is b. sovereign.

However, although the states are meant to be sovereign, there is some discussion about this: they are not perfectly sovereign, and for example the recent decision of the Supreme Court overrode the solutions of single states with respect to marriage equality.

Yes all of them are right