The drought alone did not cause the dust bowl. It was a combination of several things, the drought and

A) over-grazing by livestock and poor farming techniques.

B) the planting of farm crops in place of the native grasses.

C) high spring and summer temperatures and the decline of the bison.

D) the development of the railroad and highway system throughout the country.

The correct answer is letter A

Perhaps the greatest environmental disaster in the history of the United States is not the 21,000 tonnes of dioxin and other industrial waste buried in Love Canal, near Niagara Falls, between the 1950s and 1970s. Nor the accident with the Deepwater Horizon platform in 2010 , which spilled oil into the waters of the Gulf of Mexico. The story of the Dust Bowl - the misery caused by dust storms generated by the removal of grass and buffaloes that held the soil of the United States' crude - is the country's great forgotten environmental tragedy.

d. migration of french settlers into english colonies