请教一道逻辑题

locklv

49.    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.

答案貌似是B

locklv

顶，请帮忙看一下，不是很明白。。。。

basking

1975-1985 美国铅污染水平下降,联邦政府要求降低铅生产的法令1975年就开始实施了,但是1975-1985间铅污染水平下降是因为减少75%的含铅汽油,问支持的理由

B:大多数的铅污染水平下降现象1976年前就有了,但是主要的江水含铅水平下降是在1980-1985年之间

所以支持结论,不知道我个人理解的对不对

locklv

为什么汽油是5年以后体现出来，而工业排放在76年立刻就见效。。。这里面有什么常识吗。。。

naughtyboy

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?
以下哪个说明因为leaded gas所以污染下降

B：废弃物下降从76年之前开始，但是80年后污染开始大幅下降

说明废弃物减少不是大幅下降的原因，排除他因

仙蒂瑞拉

没有常识的。这里要是写2.3.4年也行的。

美国人的思维是：不管其充分性。要是x选项能使结论更加可信,那x选项就是正确的。

christete

纠结我好久