单项选择题

Because humans are at the top of the food chain, they are particularly vulnerable to the effects of nondegradable (不可能降解的)pollutants. This was clearly illustrated in the 1950s and 1960s when residents living near Minamata Bay, Japan, developed nervous disorders, shaking, and paralysis(瘫痪，麻痹) in a mysterious widespread. Over 400 people died before authorities discovered that a local industry had released mercury(水银，汞) into Minamata Bay. This highly toxic element stored up in the bodies of local fish and eventually in the bodies of people who consumed the fish. More recently research has revealed that many chemical pollutants are harmful to the human beings.
Pollution also has a dramatic effect on natural resources. Ecosystems such as forests, wetlands, and rivers perform many important services for the earth’s environment. They improve water and air quality, provide living places for plants and animals, and provide food and medicines. Any or all of these ecosystem functions may be impaired or destroyed by pollution. Moreover, because of the complex relationships among the many types of organisms and ecosystems, environmental pollution may have far-reaching consequences that are not immediately obvious or that are difficult to predict. For instance, scientists can only point out some of the potential impacts of the decrease of the ozone layer(臭氧层), the protective layer in the atmosphere that shields the earth from the sun’s harmful rays.

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