From your description of the situation, you were a resident of DC for all of 2015. Having and living at a second home in another state does not mean you changed your state of residence. In the Personal Info interview, list DC as your state of residence and do not select "Lived in another state in 2015". That question only applies when you changed your state of residence. What makes you a resident of a state (or country)? Generally, you're a resident of a state (or country) if you intend to either stay there permanently, or return there after a temporary absence. It's where home is – where you come back to after being away on vacation, business trip, overseas or out-of-state employment, or school. Many factors are considered, not the least of which are where you are registered to vote, own homestead property and are licensed to drive.
