According to the Textbook,in Repeated Experiments When a $20 Bill

According to the textbook,in repeated experiments when a $20 bill is auctioned such that the two top bids pay the auctioneer and then the top bid receives the $20 bill,the _______ because _________

A) top bid is $1;students bid in increments of $1.
B) top bid is $10;the total cost is then $20.
C) Sum of the top two bids frequently exceed $50;the bidder with the second place bid raises the bid and hopes the other bidder quits.
D) top bid is $20;the $20 bill is worth exactly $20.