Directions: Complete the following passage by filling in each blank with ONE word that best fits the context.
New studies show how food and its production affect the globe and its climate. The process of making a hamburger, for example, requires lots of energy. A cow has to be fed and raised on farmland. And cow waste is a major source of methane（沼气）—  48 especially powerful greenhouse gas. The cow has to be killed. The meat has to be processed and shipped,   49 takes fuel. Most of the cow won’t even be used for meat people eat. By the time a hamburger finally lands on a dinner plate,   50 has made bad effect on the environment.
We can reduce the production of global warming gases by eating less beef. Other kinds of meat like pork and chicken do  51 harm to the environment ---at least  52 terms of the amount of greenhouse gases released.   53 , all kinds of meat are harder on the planet than vegetables.  54 changing our diet to less meat and more vegetables, as it turns  55 , may do the world some good.