In simple terms, Le Chatelier's Principle tells us that a reaction at equilibrium will shift in such a way as to undo what we do to it. Therefore, if we decrease A, it will try to undo that. How can it? It will try to increase A. How can it do that? It will shift to the left BECAUSE that direction takes C and produces A and B. The other two work the same way. I shall be happy to check your work. Just an answer won't do. You need an explanation, too.
