If scientists were able to stop the techonic plates from moving, people on earth would no longer have

Earthquakes

The movement of the tectonic plates causes earthquakes. There are different kinds of plate interactions, but basically it's like a rubber band being stretched then the energy is released in the form of the ground shaking.

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.