London’s "killer fog" or The Great Smog of London was the extreme event of air pollution in London. Millions of coal fires and stagnant air were the prime reason for the event.
The Great Smog of London was one of the worst events of the air pollution that engulfed the city of England. The industrial air pollutants of the burning coal and high-pressure weather circumstances made the city covered in smog.
This event caused many deaths due to pneumonia and bronchitis in people. The burning of the coal in the industrial plants of the city was the major reason for the smog.
Therefore, option B. millions of coal fires and stagnant air were the main reason for the great smog of London.
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