【正确答案】 A

【答案解析】[听力原文]
The climate in the United States varies from coast to coast. Temperatures change from 20 degrees centigrade below zero in winter to nearly 25 degrees centigrade above zero in summer. Taking the country as a whole, we may classify the climate in the country as one of the continental or as one of the mild subtropical.
The southwest and California have warmer climates with moist air, but in the western plateau including Nevada, Arizona,. Utah and parts of Idaho and Colorado, days are hot and nights cool. The weather is dry and there is little rain for the breezes of the Pacific lose their moisture as they hit the mountains.
In the northeast and the areas around the Great Lakes, the weather is hot in summer and cold in winter. There is much rain and snow. The Gulf Plain and the southeastern part enjoy warm weather and moist air. In the central plain the weather is hot in summer and cold in winter during which there is much snow.
Almost through the middle of the country, north and south, runs a well-known 50-centimeter Rainfall Line, in the east of which there is more rain so agriculture is easy; but in the west of which there is much less rain with the exception of the coastal areas along the Pacific. These areas are especially favoured by the prevailing wind, which gather the rains as they leave the ocean.
The Cascade and the Sierra Nevada Mountains, due to their locations close to the coast, catch the largest share of rain coming from the ocean before it comes to further inland. So there is too little rain available for almost the whole western half of the country.