Answer:
B) subway trains
Explanation:
On December 5, 1952, during a bitter winter, London encountered a strange mist that seemed to increase in size and intensity more and more. This fog began to take over the city and take on a frightening color, especially when it was mixed with smoke and soot produced.
factory smokestacks, home chimneys and car exhaust, which made the fog a huge threat to the air and the breath of Londoners. The fog was so devastating that it killed up to 12,000 people.
