Reason for endothermic nature of NaHCO3 + C2H4O2 reaction
Your "all of the above" answer is correct, with emphasis on number 2.  The phase change from a condensed phase (solid or liquid) to gas is almost always endothermic.  It's the same thing as wetting your hand then blowing on it.  The liquid water undergoes and endothermic phase transition which takes in heat from its surroundings, i.e. it evaporates and your hand gets cold.