Since the passage of the state’s Clean Air Act ten years ago, the level of industrial pollutants in the air has fallen by an average of 18 percent. This suggests that the restrictions on industry embodied in the act have worked effectively. However, during the same period the state has also suffered through a period of economic decline. The number of businesses in the state has fallen by 10 percent, and the number of workers employed has fallen by 12 percent. It is probable that the business decline, rather than the regulations in the act, is responsible for at least half of the decline in the pollution.

12. Which of following is an assumption made in the passage above?

(A) Most businesses in the state have obeyed the regulations embodied in the Clean Air Act.

(B) The economic decline of the state can be attributed, in part, to the effects of the Clean Air Act.

(C) The amount of air pollution in a given area is likely to be proportional to the number of businesses and workers active in that area.

(D) The restrictions on business activity in other states are less stringent than are those embodied in the Clean Air Act.（C）

(E) The Clean Air Act has been only very slightly successful in achieving the goal of reduced air pollution.

为什么Ｂ不对呢？我觉得Ｂ比Ｃ　更恰当一些