Moving to another question will save this response. Question 4 of 18 Question 4 2 points Saved In a common value auction O a. everyone knows that the item has a given unknown market value O b. each person has their own private valuation not necessarily equal to the market value, but these private valuations are the same for all participants O c each participant estimates the unknown common market value . d.both a and c are true > Moving to another question will save this response.