crackinggmat wrote:15. The level of lead contamination in United States rivers declined between 1975 and 1985. Federal regulations 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 rives 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 contamination occurred between 1980 and
1985.
(C) Levels of lead contamination in rivers fell sharply in 1975-1976 and rose very slightly over the next nine years.
(D) Levels 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.

b

crackinggmat wrote:15. The level of lead contamination in United States rivers declined between 1975 and 1985. Federal regulations 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 rives 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 contamination occurred between 1980 and
1985.
(C) Levels of lead contamination in rivers fell sharply in 1975-1976 and rose very slightly over the next nine years.
(D) Levels 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.

I like the question.

I was confused b/w B and E

Actually both are good contenders. I don't know why somebody mentioned E as irrelevant.

So

Analyze this----

X= Decline in lead discharge
Y= Decline in lead gasoline usage
Z= Decline in lead in RIVERS

Premise says that

X causes Z

Conclusion says that

Y causes Z

We need to support the conclusion

B says that when X happens then Z does not happen.

Precisely, X and Z do not happen in same time frame so the casual relationship is not possible.
X happens before 1976 whereas Z happens after 1980.

So this eliminates the likelihood that X caused Z.

THIS IS A STRONG CASE

NOW there is a weaker version of strengthener also....E

E validates the data that YES there was 75% decline in lead gasoline usage but creates very minimal impact on the conclusion. We will have a hard time to prove that X did not cause Z, though Y is there.

B kicks E out







b