Conc: The device can radically improve emergency teams' ability to locate quickly people who are trapped within the wreckage of collapsed buildings.
(A)
People trapped within the wreckage of collapsed buildings usually have serious injuries that require prompt medical treatment - Probably the reason why the device is required, but doesn't substantiate whether it will be able to detect people trapped under building wreakage.
Drop(B)
The device gives a distinctive reading when the signals it detects come from human beings rather than from any other living beings. This option eliminates a possible alternate cause for the weak electromagnetics signals. If it did pick-up signals from other living beings, say a pet, then the conclusion does weaken.
Keep(C)
Most people who have survived after being trapped in collapsed buildings were rescued within two hours of the building's collapse - We probably want to reduce this further. Doesn't explain how the device would help locate trapped individuals successfully.
Drop(D)
Ultralow-frequency signals are not the only electromagnetic signals that can pass through almost any physical obstruction. Maybe the case, however, we're told that the only ultralow-frequency signals picked up by the devices are those identified as beating heart. We need not bother with other types of ultralow frequencies.
Drop(E)
Extensive training is required in order to operate the device effectively - Maybe the case, but doens't help us understand how it supports quick discovery of trapped individuals.
Drop