Clay is important because it is used to make containers of all kinds. Workers add water to soften clay. This makes it easier to form into shapes by machine. Then it is heated to a very high temperature. The result is a container that will last for many years.
In many countries, clay was formed from volcanoes（火山）. This kind of clay usually contains many minerals（矿物质）. So the fires to make containers from volcanic clay must be hotter that those used for non-volcanic clay. The fires may be as hot as 1400℃. The high temperature should not be reached too fast so that the containers can be dried slowly.
You can add some materials to clay to gain desired results. For example, you can add sand to prevent tiny breaks or lines from forming on the surface of the final product. But you should not use sand from the coasts of oceans. Instead, you should use sand from rivers or other areas.
Clay often exists in fields covered with some water. The clay will be found about one meter below the ground. River banks often also have clay about one meter or less under the surface. Clay is very shiny when it is wet. You can also take some of the material and add enough water to it. Then press it in your hands until it is about the size of an egg. It is probably clay if it holds together when you stop pressing. 【題組】43. What do workers do with clay to make it into different shapes?
(A) Soften it by putting water into it.
(B) Heat it to a very high temperature.
(C) Harden its surface by pressing it.
(D) Add some materials into it.
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