4. All bidders in a second price auction have private independent values vi{0,1}, each value realizes with equal probability. (a) Suppose there are two bidders, show that he seller's expected revenue (that is, how much the winner pays the seller on average) is 1/3. (b) What is the seller's expected revenue if there are three bidders? (c) Explain why the seller's expected revenue increases as the number of bidders increases