单项选择题

Question 11-15 are based on the following passage:
  Firefighters are often asked to speak to school and community groups about the imprtance of fire safety,particularly fire prevetion and detecton.Because smoke detectors reduce the risk of dying in a fire by half,firefighters often provide audiences with information on how to install these protective devices in their homes.
  Specifically,they tell them these things:A smoke detector should be placed on each floor of a home.While sleeping,people are in particular danger of an emergent fire,and there must be a detector outside each sleeping area.A good site for a detector would he a hallway that runs between living sapces and bedrooms.
  Because of the dead-air space that might be missed by hot air bouncing around abovea a fire,smoke detectors should be installed either on the ceiling at least four inched from the nearnest wall,or high on a wall at least four,but no further than twelve,inches from the ceiling.
  Detectore should not be mounted near windows,entrances,or other places where drafts（过堂风）might direct the smoke away from the unit.Nor should they be palced in kichens and garages,where cooking and gas fumes are likely to cause false alarms.
 

The passage implies that dead-air space is most likely to be found（）.

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