At the end of 1997 several nations stated that their oil reserves had not changed since the end of 1996. But oil reserves gradually drop as old oil fields are drained and rise suddenly as new oil fields are discovered. Ttherefore, oil reserves are unlikely to remain unchanged from one year to the next. So most of the nations stating that their oil reserves were unchanged are probably incorrect. Which one of the following is an assumption the argument requires? ["For any nation with oil reserves, it is more likely that the nation was mistaken in its statements about changes in its oil reserves than that the nation's oil reserves remained unchanged.", 'It is likely that in 1997, in most of the nations that stated that their oil reserves were unchanged, old oil fields were drained or new oil fields were discovered, or both.', 'If a nation incorrectly stated at the end of 1997 that its oil reserves had not changed since the end of 1996, then during 1997 that nation drained its old oil fields and discovered new ones.', "If a nation's oil reserves change from one year to the next, then that nation is obligated to report the change correctly."]