Расположите пропущенные предложения в таком порядке, чтобы получился связный текст.
Nowadays suspended ceilings have become a very popular and economical feature in many types of buildings. 1_______. Many of them install and maintain complex mechanical and electrical installations above the ceiling. These installations include air conditioning ducts, water and waste piping and electrical and communications wiring. 2_______. All these ducts and pipes occupy a considerable space in the building. In some of them they may be equal to the amount of their living space.
3_______. Lighting fixtures, loudspeakers, and fire detection devices may also be installed into a ceiling. 4_______.
The most numerous among these buildings are office and laboratory structures
They also include such services as fume ducting, vacuum piping, fuel gas lines, compressed air lines, water piping, and chemical waste piping
Ducts, pipes and conduits can be placed in the space between the ceiling and the structure
Many such constructions can serve as membrane fire protection for the floor and roof structure above