求助 lsat-14-2-24

24. A certain airport security scanner designed to detect explosives in luggage will alert the scanner's operator whenever the piece of luggage passing under the scanner contains an explosive. The scanner will erroneously alert the operator for only one percent of the pieces of luggage that contain no explosives. Thus in ninety-nine out of a hundred alerts explosives will actually by present.

The reasoning in the argument is flawed because the argument

(A) ignores the possibility of the scanner's failing to signal an alert when the luggage does contain an explosive

(B) draws a general conclusion about reliability on the basis of a sample that is likely to be biased

(C) ignores the possibility of human error on the part of the scanner's operator once the scanner has alerted him or her

(D) fails to acknowledge the possibility that the scanner will not be equally sensitive to all kinds of explosives

(E) substitutes one group for a different group in the statement of a percentage

答案e,请问one group 和a different group 到底是什么啊。谢谢大家。

The key is understanding. The question tries to confuse you by comparing two different group: lugguage that contains explosives and lugguage that does not contain explosive.

First it says the scanner alerts operator for 1% of pieces of lugguage that contain no explosives. The conclusion is (rephrased) the scanner alerts operator 99% of the pieces of lugguage that contains explosives.

Read it again, and think a bit harder. You will see the two sentences are not talking about that same thing