I believe the answer is: activation of large nerve fibers in your spinal cord
Gate control theory was popularized by Ronald Melzack and Patrick Wall, it views that non-painful area input closes the doors or "gates" to the painful area input, this exist in order to prevents pain sensation from coming through the central nervous system and being transferred across our body.
I’m not sure the exact page number, but it is in Chapter 1.
B sounds like a good choice to go for
There must be an earthquake detector in place to detect any earthquakes off the shores in the oceans. This system can be a regional or local system, and although the system is fallible the margin of error is very small.
Sometimes though the earth quake/movement is too close to shore to detect it in time, and people get caught in it as a result.
There also needs to be a universal warning signal that actually tells people that the tsunami is coming.
I hope this helped.
