Question ID:PT33 S1 Q25 Passage:The number of airplanes equipped with a new anticollision device has increased steadily during the past two years.  During the same period, it has become increasingly common for key information about an airplane's altitude and speed to disappear suddenly from air traffic controllers' screens.  The new anticollision device, which operates at the same frequency as air traffic radar, is therefore responsible for the sudden disappearance of key information. Stem:Which one of the following, if true, most seriously weakens the argument? Correct Answer Choice:DChoice A:The new anticollision device has already prevented a considerable number of mid-air collisions. Choice B:It was not until the new anticollision device was introduced that key information first began disappearing suddenly from controllers' screens. Choice C:The new anticollision device is scheduled to be moved to a different frequency within the next two to three months. Choice D:Key information began disappearing from controllers' screens three months before the new anticollision device was first tested. Choice E:The sudden disappearance of key information from controllers' screens has occurred only at relatively large airports.