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 be present. The reasoning in the argument is flawed because the argument ['fails to acknowledge the possibility that the scanner will not be equally sensitive to all kinds of explosives', "ignores the possibility of human error on the part of the scanner's operator once the scanner has alerted him or her", 'draws a general conclusion about reliability on the basis of a sample that is likely to be biased', 'substitutes one group for a different group in the statement of a percentage']