In older commercial airplanes, the design of the control panel allows any changes in flight controls made by one member of the flight crew to be immediately viewed by the other crew members. In recently manufactured aircraft, however, a crew member' s flight control changes are harder to observe, thereby eliminating a routine means for performing valuable cross-checks. As a result, the flight crews operating recently manufactured airplanes must inform each other verbally about flight control changes much more frequently. The statements above, if true, most strongly support which one of the following? ["How frequently an airplane's flight crew members will inform each other verbally about flight control changes depends in large part on how long it takes to perform those changes.", 'How often flight crew members must share information verbally about flight control changes depends in part on what other means for performing cross-checks are available to the crew.', 'The flight crew members operating a recently manufactured airplane cannot observe the flight control changes made by other crew members by viewing the control panel.', 'In recently manufactured aircraft, the most valuable means available for performing cross-checks involves frequent verbal exchanges of information among the flight crew members.']