请教一题

mariezhu

A chemical company claims that, since only one of 520 rats that were given high doses of a new artificial sweetener developed cancer while all the others remained healthy, the sweetener is not carcinogenic for human beings and ought to be approved for human consumption.
Which of the following, if true, most strongly supports the chemical company’s claim?

(A) Chemicals that are carcinogenic for rats are usually also carcinogenic for other animals, such as guinea pigs, used in experiments.
(B) The spontaneous incidence of cancer in this particular strain of rat is approximately one in 540.
(C) Tests conducted on a certain strain of mouse show that, of 500 mice given a dose of sweetener similar to that given the rats, 53 developed cancer.
(D) Certain chemicals that are carcinogenic for human beings have been shown not to be carcinogenic for rats.
(E) The average lifespan of the strain of rat used in the experiment is 2 years; the chemical company terminated the experiment when the rats were 13 months old.

请教答案及思路,多谢

mindfree

I pick B.

dmqyql

After the comparison, I feel that A is better than others. C, D oppose the claim.

robertchu

Agree on B.
B basically provides a controlled reference group -- rats in the same strain without exposure to the sweeter.