Physics
Why do birds not have respiratory trouble at the time of flying at high altitude ?

They have extra air sacs
They fly inactively
They use less oxygen
Their lungs are very large

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Physics
Lightning is produced when

Strong opposite charges in different clouds break down the resistance offered by the intervening air
Similar charges of electricity rush towards each other and then get repelled
Water vapour produces electricity in the clouds
Clouds strike against impurities in air and the friction burns up these impurities

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