Global ecological problems reduce to the problem of balancing supply and demand. Supply is strictly confined by the earth' s limitations. Demand, however, is essentially unlimited, as there are no limits on the potential demands made by humans. The natural tendency for there to be an imbalance between demand and sustainable supply is the source of these global problems. Ttherefore, any solutions require reducing current human demand. Which one of the following is an assumption on which the argument depends? ['Human consumption does not decrease the environmental supply.', "Actual human demand exceeds the earth's sustainable supply.", "It is possible to determine the limitations of the earth's sustainable supply.", 'Supply and demand tend to balance themselves in the long run.']