I would go with the most popular searched term out of A.com, B.com, and C.com. Google obviously gives more preference to .com domains. Then I would do as directed above, linking with the appropriate text for A, B, and C. If the most popular searched term is A then you will not have to establish as many links with keyword A as you will for the keywords B and C. to achieve the best results for all three. I would also register B.com and C.com and 301 redirect them to A.com just to keep them out of the competitions hands. That's my take.
Headstones U.S.A. Discount grave memorials and monuments