A、The natural force makes it come into being. B、It originates from some chemical elements in the nature. C、It comes from the roc

Clay is found almost everywhere in the world. (32) It is formed by the action of wind and water on rocks over thousands of years. The rocks change in both chemical and physical ways. Chemically, elements are added and taken away. Physically, the rocks break down into smaller and smaller pieces. After a long time, some of the rock changes to clay. (33) Clay is important because it is used around the world to make containers of all kinds. Potters add water to soften the clay. This makes it easier to form into shapes by hand or by machine. Then it is fired in an extremely hot stove. The result is a container with a hard surface that will last for many years. You can usually find good clay (34) in low areas of islands or land, especially if volcanoes helped form the land. (34) Clay often exists in fields covered with some water. The clay will be found about one meter below the ground. (34) River banks often also have clay about one meter or less under the surface. You can recognize clay (35) because it is very shiny when it is wet. You can also perform a test. Take some of the material and add enough water to it to make it seem like you are making bread. Then press it in your hand until it is about the size of an egg. It is probably clay if it holds together instead of falling apart when you stop pressing.