Difficulty is defined by (a) frequency of use, (b) frequency of spelling pattern, and (c) developmental norms. It is not difficult, then, for teachers to place students with words of appropriate difficulty based on simple measures of instructional level (Schlagal, 1996).
If one assumes that shifts in the supply curve of ethanol are solely due to the changing price of corn, then, up to an ethanol price of $2.90, the price of corn completely determines the price of ethanol. In other words, the price of corn drives the price of ethanol, not the other way around. This is actually quite logical since the amount of ethanol used is essentially fixed; consequently, something else must be driving the price of ethanol.
Quick Answer. Ethanol is added to gasoline because it is a renewable source of energy and helps to decrease carbon emissions and reduce America's energy dependence on other countries. It also acts as an oxygenating agent, which reduces carbon monoxide and soot emissions produced when fossil fuels are burned.