Emissions from automobiles that burn gasoline and automobiles that burn diesel fuel are threatening the quality of life on our planet, contaminating both urban air and global atmosphere. Ttherefore, the only effective way to reduce such emissions is to replace the conventional diesel fuel and gasoline used in automobiles with cleaner-burning fuels, such as methanol, that create fewer emissions. Which one of the following is an assumption on which the argument depends? ['Reducing the use of automobiles would not be a more effective means to reduce automobile emissions than the use of methanol.', 'Automobile emissions constitute the most serious threat to the global environment.', 'At any given time there is a direct correlation between the level of urban air pollution and the level of contamination present in the global atmosphere.', 'If given a choice of automobile fuels, automobile owners would not select gasoline over methanol.']