The answer is Faults are storing elastic strain. To simplify, seismic gaps are places where scientist think that faults are keeping elastic strain. In addition, scientists think that stress on a fault constructs up to a critical point and is then unconstrained as an earthquake. The seismic gaps are areas in which no earthquakes have occurred over a long period of time and therefore are probable to be under a high volume of stress.
The right option is; b. the water caused an increase in temperature of the air inside the ball and an increase in pressure.
The dent (hollow area formed by pressing or hitting) from the ping-pong ball disappeared because energy was transferred from the hot boiling water in which the ball was placed to the air inside the ball. This transferred energy will increase the temperature of the air inside the ball and the air molecules will begin to move faster with a greater force. Hence, causing an increase in pressure.