Modern navigation systems, which are found in most of today' s commercial aircraft, are made with low-power circuitry, which is more susceptible to interference than the vacuum-tube circuitry found in older planes. During landing, navigation systems receive radio signals from the airport to guide the plane to the runway. Recently, one plane with low-power circuitry veered off course during landing, its dials dimming, when a passenger turned on a laptop computer. Clearly, modern aircraft navigation systems are being put at risk by the electronic devices that passengers carry on board, such as cassette players and laptop computers. Which one of the following, if true, LEAST strengthens the argument above? ['No problems with navigational equipment or instrument dials have been reported on flights with no passenger-owned electronic devices on board.', 'After the laptop computer was turned off, the plane regained course and its navigation instruments and dials returned to normal.', 'Planes were first equipped with low-power circuitry at about the same time portable electronic devices became popular.', 'When in use all electronic devices emit electromagnetic radiation, which is known to interfere with circuitry.']