Read the following Passage and answer the following questions.

One of the main tenets of the plate tectonics theory is that plates move as somewhat rigid units relative to all other plates. As plates move, the distance between two locations on different plates gradually changes. Major interactions of plates occur along their boundaries. They make three types of boundaries- convergent plate boundaries; divergent plate boundaries and transform plate boundaries. The continental drift theory, conventional currents concept and sea floor spreading concept provided the base for the theory of plate tectonics. It explains formation of first and second order landforms. It explains several other phenomena such as mountain building, sea floor trench formation, volcanism, and seismicity.