Read the following passage then choose the best answer A, B, C or D.

I often hear or read about “natural disasters” - the eruption of  Mount St Helen (a volcano in  the state of Washington), Hurricane Andrew in Florida, the floods in the American Midwest, terrible earthquakes all over the world, huge fires and so on. But I’ll never forget my first personal experience with the strangeness of nature – “the London Killer Fog” of 1952. It began on Thursday, December 4th when a high-pressure system (warm air) cover southern England. With the freezing-cold air below, heavy fog formed. Pollution from factories, cars, and coal stoves mixed with the fog. The humidity was terribly high and there was no breeze at all. Traffic (cars, trains, and boats) stopped. People couldn’t see and some walked onto the railroad tracks or into the river. It was hard to breathe, and many people got sick. Finally on Tuesday, December 9th, the wind came and the fog went away. But after that, even more people got sick, many of them died.