The correct answer is A. 0.
The other options are incorrect because they do not represent a signal that has extinguished. Option B, 00, represents a signal that is still on. Option C, ——00, represents a signal that is not on and has never been on. Option D, 00, represents a signal that is not on but was on at some point in the past.
A signal that has extinguished is a signal that is no longer on. This can happen for a number of reasons, such as the signal being turned off, the power being cut to the signal, or the signal being blocked by something. When a signal extinguishes, it will typically stop emitting any light or sound.
In the context of the question, the signal is likely a light or sound that is used to warn people of danger. When the signal extinguishes, it means that the danger is no longer present.