In 2022, Rainer disposed of some crypto he had held for several years. He is not entirely sure of his basis in the coins. How can he best determine the original purchase price in order to minimize the tax impact of the sale? A. An estimate is fine. As long as Rainer knows roughly what the coins were selling for the month he made the purchase, he can use that as a range. B. The coin exchange Rainer uses is responsible for providing that information, so he can contact them and find the original purchase price. C. If he doesn't have the original records, he cannot recreate them. Rainer must use a $0 basis. D. Rainer can use a Blockchain explorer to determine the date and time of his purchase and the fair market value (FMV) of the coins at that time.