Tube is a hollow cylinder which can be very long. It is used to transfer materials from one place to another, such as water and it is often called a pipe.
If made of glass it can be a test tube or a fluorescent one, if it is metal it can be the exhaust pipe of a car, or for water, etc. It can also be made of cardboard, ceramic or other materials.
Each has its use. Many are sealed at one end and others have a lid opening, which can be removed or replaced; there are tubes for creams, glues, paints etc.
Tubes may be flexible or rigid, for instance a hose to water plants is flexible, while a tube for moving cement and many other products is rigid.
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