The name Sahara derives from the Arabic word for "desert" or "steppe". At 3.5 million square miles, an area roughly the size of the United States, the Sahara Desert in northern Africa is the largest desert in the world. It spans the continent from the Atlantic Ocean to the Red Sea. Daytime temperatures can reach as high as 130~F. The humidity sometimes gets into the teens. But it can also be as low as 2.5 percent, the lowest in the world. Most of the Sahara receives less than five inches of rain per year, while large areas sometimes have no rainfall at all for years.
At the heart of the Sahara is the landlocked north African country of Niger. Here the sand dunes can be 100 feet tall and several miles long. Here sand plains stretch over an area larger than Germany where there is neither water nor towns. Yet sitting in the midst of the surrounding desert is the town of Bilma. Suddenly there are pools of clear water. Surprisingly, there are groves of date palms. Underground water resources, or oases, sufficient to support irrigated agriculture are found in dry stream beds and depressions. Irrigation ditches run off a creek to water fields. Corn, cassava, tea, peanuts, hot peppers, and orange, lime, and grapefruit trees grow in these fields. Donkeys and goats graze on green grass.
The Sahara of Niger is still a region where you can see a camel caravan of 500 camels tied together in loose lines as long as a mile, traveling toward such oasis towns. There a caravan will collect life-sustaining salt, which is mined from watery basins, and transport it up to 400 miles back to settlements on the edges of the desert. The round trip across the vast sands takes one month.
单选题
The phrase "an area roughly the size of the United States" gives an indication of the size of ______.
【正确答案】
C
【答案解析】第一段的第二句话提到“At 3.5 million square miles, an area roughly the size of the United States, the Sahara Desert in northern Africa is the largest desert in the world.”，the Sahara Desert是本句的主语，可见撒哈拉沙漠的面积大概相当于美国的大小，所以选C。