C is the initial solution, because naoh has not been added yet
B is the midpoint of the titration. naoh has been added to the solution, but it has not fully reacted yet. You can tell that this one is the midpoint because there is still HF- in the diagram, which is not one of the products formed in the reaction.
A is the endpoint because the diagram shows that all products are fully formed. There is an increased amount of Na+ and H2O in the diagram and no HF- left.
PS. I tested this answer on the concentration of acetic acid post-lab (from mcgraw hill) earlier today and it said this was the right answer :) hope this helps
