Shared setup (chef and ingredients): A chef is preparing a recipe using four ingredients out of six liquids. Two of these ingredients must come from the taste group A, B and C, and the other two must come from the group W, X, Y and Z. Three combinations are never allowed: B with W, C with Y, and Y with Z.
Which of the following must always be true?
I. If C is used, W must be added
II. If Y is used, B must be added
III. If C is not used, W cannot be added