In Wareland last year, 16 percent of licensed drivers under 21 and 11 percent of drivers ages 21-24 were in serious accidents. By contrast, only 3 percent of licensed drivers 65 and older were involved in serious accidents. These figures clearly show that the greater experience and developed habits of caution possessed by drivers in the 65-and-older group make them far safer behind the wheel than the younger drivers are. Which of the following is an assumption on which the argument depends? ['There is no age bracket for which the accident rate is lower than it is for licensed drivers 65 and older.', 'The difference between the accident rate of drivers under 21 and of those ages 21-24 is attributable to the greater driving experience of those in the older group.', 'Drivers 65 and older are less likely than are drivers 24 and younger to drive during weather conditions that greatly increase the risk of accidents.', 'Drivers 65 and older do not, on average, drive very many fewer miles per year than drivers 24 and younger.']