【B1】 【B4】

Now we travel to the north central part of the United States. We are in the state of South Dakota. The land is big and mostly flat with many  fields of com, wheat and soybeans. But as we travel west, the cropland gives way to wild grasses. A strong dry wind blows  continuously from the west.
   Suddenly, the land becomes  torn and rocky, dry and dusty--no longer green and gold. It is now a light red-brown color. All around are broken  disordered forms. There are hills and valleys of all sizes and strange shapes.
   These are the Badlands. Hundreds of thousands of years ago the area was  grassland, but, then, forces of nature  destroyed the grass. Water and ice cut into the surface of the earth. They beat at the rocks,  wearing them away. The result is one of the world’s  strangest sights.
    All together, the Badlands cover more than fifteen thousand square kilometers. About ten percent is national parkland.
   The area is a study in extremes. Temperatures in the summer have been as high as forty-six degrees Celsius.  In the winter they have dropped to as low as forty-one degrees below zero.
   Life in the Badlands is difficult, but animals do survive. The most well known is the prairie dog.  This small mammal lives in a series of underground passages.