SAP智力題 Auction ★★★★★★★★★

Three vases would be sold one by one in an auction, each of them is worth of 2 million dollars, but 2 of them together will be worth of 8M, if someone has got 3 of them, they would be worth of 18M. They are 3 buyers, A, B, C. They have 16M, 18M, 20M respectively. And they must bid in the order A-B-C. The bid must be integer times of million. They are very clever, and they would rather lose money as long as the loss is less than the possible profit won by others. What would be the auction result?
----Designed by Hansen Chen in 2008( https://www.sdn.sap.com/irj/scn/forum?forumID=410 )