单项选择题

There will be a steady trend toward vegetarianism. A given quantity of ground can provide plant food for man or it can provide plant food for animals which are later killed for meat. 　　In converting the tissues of food into the tissues of the feeder, up to 90 per cent is used for reasons other than tissue maintenance and growth. This means that one hundred pounds of plant food will support ten pounds of human tissue―while one hundred pounds of plant food will support ten pounds of animal tissue, which will then support one pound of human tissue. In other words, land devoted to plant food will support ten times as many human beings as land devoted to animal food. 　　It is this (far more than food preferences or religious directions ) that forces overcrowded populations into vegetarianism. And it will be the direction in which the United States of 2001 will be moving―not by presidential order, but through the force of a steady rise in meat prices as compared with other kinds of food. 　　This, in turn, will come about because our herds will decrease as the food demand causes more and more meadow to be turned to farmland, and as land producing corn and other animal food is converted to providing food directly for man. 　　Another point is that it is not only energy that is in short supply. A shortage of oil means a shortage of plastics; a shortage of electricity means a shortage of aluminium. We are also experiencing a shortage of paper and most other raw materials. 　　This means that, for one thing, our generosity in wrapping, bagging and packaging will have to recede. There will have to be at least a partial return in supermarkets to the old days where goods were supplied in bulk and given out in bags to order. It may even become necessary to return bags, as we once returned bottles, or pay for new ones. 　　A decline in per-capita energy use will make it necessary to resort to human muscle again, so that the delivery man will make a comeback (his price added to that of the food, of course).Since energy shortages will cause unemployment in many sectors of the economy, there will be idle hands to do the manual work that will become necessary. 　　From an energy-saving standpoint, it would make far more sense to order by phone and have a single truck deliver food to many homes, than for a member of each home to drive an automobile, round-trip, to pick up a one-family food supply. 　　To be sure, it will not all be retrogression. Even assuming that Earth is in a desperate battle of survival through a crisis of still rising population and dwindling energy reserves, there should still continue to be technological advances in those directions that don’’t depend on wasteful bulk use of energy. There will be continuing advances in the direction of "sophistication", in other words. According to the author, deficiency of food inevitably leads to