Bunuel
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?
A. After the laptop computer was turned off, the plane regained course and its navigation instruments and dials returned to normal.
B. When in use all electronic devices emit electromagnetic radiation, which is known to interfere with circuitry.
C. No problems with navigational equipment or instrument dials have been reported on flights with no passenger-owned electronic devices on board.
D. Significant electromagnetic radiation from portable electronic devices can travel up to eight meters, and some passenger seats on modern aircraft are located within four meters of the navigation systems.
E. Planes were first equipped with low-power circuitry at about the same time portable electronic devices became popular.
OFFICIAL EXPLANATION
The conclusion of the argument is based on the causal assumption that electronic devices cause a disturbance in low-power circuitry, creating an obvious danger:

The question stem is a Strengthen (remember, Least works like Except in question stems) and thus the four incorrect answers will each strengthen the argument. As you attack the answer choices, look for the five causal strengthening answer types discussed earlier.
Answer choice (A): This answer choice strengthens the argument by showing that when the cause is absent, the effect does not occur (Type C). Once the laptop was turned off, the cause disappeared, and according to the author’s beliefs, the effect should then disappear as well.
Answer choice (B): This answer strengthens the argument by showing that the data used to make the conclusion is accurate (Type E). By stating that all electronic devices emit radiation, the answer choice closes a hole in the argument.
Answer choice (C): This answer choice strengthens the argument by showing that when the cause is absent, the effect does not occur (Type C).
Answer choice (D): This answer strengthens the argument by showing that the data used to make the conclusion is accurate (Type E). By showing that radiation can travel far enough to reach the cockpit, the cause is confirmed as possible.
Answer choice (E): This is the correct answer. The fact that the circuitry and electronic devices became popular at the same time does not offer any supporting evidence to the contention that the electronic devices cause the interference with the low power circuitry. This answer has no effect on the argument and is therefore correct.
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