Heavy salting of Albritten' s roads to melt winter ice and snow began about 20 years ago. The area' s groundwater now contains approximately 100 milligrams of dissolved salt per liter. Groundwater in a nearby, less highly urbanized area, where little salt is used and where traffic patterns resemble those of Albritten 20 years ago, contains only about 10 milligrams of dissolved salt per liter. Since water that contains 250 or more milligrams of dissolved salt per liter tastes unacceptably salty, continuing the salting of Albritten' s roads at its present rate will render Albritten' s groundwater unpalatable within the next few decades. Which one of the following, if true, most seriously weakens the argument? ["Salting of Albritten's roads is likely to decrease over the next few decades.", 'Even water that contains up to 5, 000 milligrams of dissolved salt per liter is safe to drink.', "Albritten's groundwater contained roughly 90 milligrams of dissolved salt per liter 20 years ago.", 'Salting icy roads is the simplest way to prevent accidents on those roads.']