【单选题】

The Nile madeEgypt’s civilization possible. The river is more than 400 miles long. In its fertile valley crops are grown for food and cotton for clothing. Mud from the river bottom makes good bricks for houses. Thus ways of getting food, clothing and shelter were close for theEgyptians.

The Nile is a highway for the people ofEgypt. Flat bottomed boats and large narrow barges carry products from one city to another. There are also passenger boats on the Nile, carrying people up and down the river. In ancient times huge blocks of stones were floated down the river on barges. These stones are used in making buildings and monuments.
For thousands of years theEgyptians have depended on the Nile for their crops. The land on both sides of the Nile is desert, where crops cannot be raiseD、But crops grow well in the Nile Valley. In fact, several different crops are often grown on the same land during the same year.
Once the Nile flooded each year, overflowed its banks, and carried rich soil in land every summer. These floods were caused by early summer rains.
At present there is a series of dams on the Nile. Water raised high in the river each summer as usual. The people do not let the Nile flood, however. They store the water behind dams. It is now possible to use the water as needed, not just at flood time.
Which of the following can best summarize the passageA．The Nile is the source of flooD、
B．The Nile is a highway for the people inEgypt.
C．The flat bottomed boats have been useD、
D．The Nile madeEgypt’s civilization possible.