Lights----to give lightdarkness.
fans-----------produce air to feel cool.
computer----to play games,draw,search informations
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If we look around we, can see many things, which is very usefull, for us.                
some of them are
 light- which help us to see from darkness
 T.V- for an entirtanment  
fans- which cools from steaming hot etc.......
and also all sources like : fridge, computer, ...........etc .
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