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.

Which of the following, if true, would most seriously weaken the conclusion drawn in the passage above?
(A) During the last ten years, economic conditions in the nation as a whole have been worse than those within the state.
(B) Amendments to the Clean Air Act that were enacted six years ago have substantially strengthened its restrictions on industrial air pollution.
(C) Of the businesses that ceased operating in the state during the last ten years, only 5 percent were engaged in air-polluting industries.
(D) Several large corporations left the state during the last ten years partly in order to avoid compliance with the Clean Air Act.
(E) Due to its small budget, the state office charged with enforcement of the Clean Air Act has prosecuted only two violators of the law since its passage.

D is correct. This is saying that act caused air polluting businesses to leave which would also cause business decline and the air to be cleaner.

i think its D .
D doesnt strengthen the argument ....as it says business ceased to operate because of the non compliance to restrictions and not because of the economic decline .It weaknes the arguments by saying that these large corporations left because their air pollution content was so much that they could not comply with the restrictions.

C says only 5% of the pollution making industries shut down because of the decline in economy doesn't mean that they were not making significant contribution to pollution. Possibilty is that these 5 % were contibuting most to the pollution. so in C we have to assume a bit to consider it as answer.

~sara

But the regulations were directly responsible for the flight of business from the area.