Physics
Supersonic plane fly with the speed

of light
of sound
less than the speed of sound
greater than the speed of sound

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Physics
Light houses are places with powerful lights to :

Guide and warn the ships coming from different directions in the ocean
Indicate to the incoming warships, the location of a harbour during night
Guide and resolve traffic jams in crowded metro-cities during nights
Guide and help large crowds at religious gathering during nights

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