Which of the following statements best summarizes the effects of the london fog of 1952?

a.
pollution from coal fires caused over 4,000 deaths, leading the british government to change their outlook on pollution.
b.
smog caused by automobiles hung over london for three months, prompting businesses to stagger their employees' working hours.
c.
smog produced by steel mills reduced visibility in london to near zero. many businesses moved out of the city, relocating to bristol.
d.
fog produced by the overheating of the thames river blanketed the city for half a year, until steel mills diverted their hot effluent to cooling towers.