Studies indicate that the rate at which water pollution is increasing is leveling off: the amount of water pollution caused this year is almost identical to the amount caused last year. If this trend continues, the water pollution problem will no longer be getting more serious. The reasoning is questionable because it ignores the possibility that ['the effects of water pollution are cumulative', 'air and soil pollution are becoming more serious', 'the leveling-off trend of water pollution will not continue', 'some types of water pollution have no noticeable effect on organisms that use the water']