Problems caused by the leaching of pollutants from dumps and landfills are worst in countries with an annual per capita economic output of $4, 000 to $5, 000, and less severe for considerably poorer and considerably richer countries. This is so because pollution problems increase during the early stages of a country' s industrial development but then diminish as increasing industrial development generates adequate resources to tackle such problems. Ttherefore, problems caused by such leaching in Country X, where the annual per capita economic output is now $5, 000, should begin to diminish in the next few years. Which one of the following is an assumption on which the argument depends? ['Industrial development in Country X will increase in the next few years.', 'Countries surrounding Country X will reduce the amount of pollution that their factories release into the air and water.', 'No other country with a similar amount of industrial development has pollution problems that are as severe as those in Country X.', 'Within the next few years, Country X will impose a system of fines for illegal waste disposal by its industrial companies.']