Why do earthquakes happen? Scientists explain that the outside of the earth is made of a number of different plates . For example, at San Francisco the Pacific  Plate which is moving towards the northwest meets the North American Plate. The Pacific Plate is moving very  slowly-at 5. 3 centimetres a year. Sometimes these two plates stop and do not move for years. Then suddenly, they jump and an earthquake is felt. As the movement of these plates, West America near the sea has always been a bad place for earthquakes. When the 1906 earthquake happened, the Pacific Plate jumped 5-6 metres to the north. We cannot stop earthquakes, but we can do things to make sure they don't destroy  the whole of cities. First ,it is not a good idea to build houses along the lines, where two of the earth's plates join together. Second, if you think there may be an earthquake, it is better to build houses on rock not on sand. Third, you must make the houses as strong as possible. Weak buildings will fall down in an earthquake, but strong ones may stay up. Scientists explain that   _  .
the outside of the earth is made of a plate the inside of the earth is made of different plates the outside of the earth is made of lots of different plates the earth is a plate