Переведите текс с поддержкою словаря:VARIOUS TYPES OF SLEEPERS Sleepers which were

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VARIOUS TYPES OF SLEEPERS

Sleepers which were first introduced in 1855 are now employed universally. They are made of wood, steel, cast iron or concrete. The required number of sleepers is enormous, and timber is becoming scarce. Thats why sleepers of other materials are widely used in many countries. Metal sleepers find a wider application in Britain; wooden sleepers last about 20 years in the main tracks, and then they give further service in sidings. Cast iron sleepers are little used because metal is very expensive everywhere. In our country concrete sleepers are being used increasingly, especially in Metro construction. Concrete sleepers have the advantage of material which withstands corrosion and rotting.
concrete - бетон
cast iron чугун
siding запасной путь