题目内容：

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In the 19th century, Americans from the eastern states moved out west to settle in the rich new lands along the Pacific Coast. The most difficult part of their trip was crossing “the Great American Desert” in the western part of the United States by horse and wagon.

The western desert can be very dangerous. There is little water and there are few trees. But the desert also has scenery of great beauty. Tall towers of red and yellow stone rise sharply from the flat, sandy valley floor. The scene has been photographed many times and appears in movies and on TV.

In Arizona, man-made dams across the Colorado River have made two large lakes in the middle of the dry desert country. At Lake Powell, the red stone arch of Rainbow Bridge rises high above the blue lake.

There are few roads. Many areas of Lake Powell’s shore can only be reached by boat or on foot. But hikers in this empty desert land sometimes find very old native American pictures, painted on the rocks.

In Death Valley, California, the summer temperature rises to 130°F—165°F. There is less than inches of rain each year. Death Valley is the lowest place in America---925 meters below sea level. In the 1800s, many travelers died when they tried to cross this waterless valley in the terrible heat.

Although the desert is dry and seems empty, there is plenty of life if you look closely. Snakes and rats have learned how to live in the desert heat. They live underground and come out at night, when it is cool. Plants such as cacti need very little water. When it does rain in the desert (sometimes only once or twice a year), plants grow quickly, and flowers open in a single day. For a short time, the desert is covered with brilliant (very bright) colors.

67．In the 19th century, Americans moved from east to west because they            .

A．enjoyed the trip                     B．wanted to make their home there

C．wanted to find new grassland there      D．had no water to drink

68．From this passage. we can conclude that         .

A．the western desert is a good place for people to live in

B．there is little water but there are many trees in the desert

C．the desert is dangerous but it is full of beauty

D．till now, people know little about the desert

69．In the 1800s, many travelers died in Death Valley because of            .

A．illness             B．high temperature

C．cold weather           D．poisonous water

70．In the desert, animals will die           .

A．if they move about                 B．if they can’t make holes underground

C．if they come out at night            D．if they drink much water