A recent test of an electric insect control device discovered that, of the more than 300 insects killed during one 24-hour period, only 12 were mosquitoes. Thus this type of device may kill many insects, but will not significantly aid in controlling the potentially dangerous mosquito population. Which one of the following, if true, most seriously weakens the argument? ['Many of the insects that were killed by the device are mosquito-eating insects.', 'A careful search discovered no live mosquitoes in the vicinity of the device after the test.', 'The device does not succeed in killing all of the insects that it attracts.', 'A very large proportion of the insects that were attracted to the device were not mosquitoes.']