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The level of lead contamination in United States rivers declined between 1975 and 1985. Federal legulation requiring a drop in industrial discharges of lead went into effect in 1975, but the major cause of the decline was a 75 percent drop in the use of leaded gasoline between 1975 and 1985.

Which of the following, if true, best supports the claim that the major cause of the decline in the level of lead contamination in United States river was the decline in the use of leaded gasoline?

A The level of lead contamination in United States rivers fell sharply in both 1975 and 1983

B Most of the decline in industrial discharges of lead occurred before 1976, but the largest decline in the level of river contamnation occured between 1980 and 1985

C Level of lead contamination in river fell sharply in 1975-1976 and rose very slightly over the next nine years.

D Level of lead contamination rose in those rivers where there was reduced river flow due to drought

E Although the use of leaded gasoline declined 75 percent between 1975 and 1985,80 percent of the decline took place in 1985.

ans:B

but I think B can eliminate that the decline of lead contamination is not due to the requirement but can not include that the main clause is the decline use of leaded gasoline.