面对干旱，各地多次适时实施人工增雨增雪作业，即通过向空中喷洒“干冰”来实现。那么喷洒“干冰”的作用是：（ ）
A．使空气液化
B．使空气中的小水珠汽化
C．使空气中的水蒸气液化或凝华
D．“干冰”熔化变为雨水
答案：C
题目分析：要解答本题需掌握：干冰升华吸热，空气中的水蒸气遇冷液化或凝华。因此，干冰只是起到升华吸热的作用，然后空气中的水蒸气受冷液化才能形成降雨。故答案选择：C
点评：题主要考查学生对：升华吸热，以及温度降低可以使气体液化、凝华的理解和掌握情况，是一道基础题。
| 任务阅读。阅读短文，根据短文内容完成表格。 | ||||||||||||||
| Mary is a student in a nursing school. She is going to graduate next month. She has two job offers. One is in a city hospital, and other is in a country hospital. The hospital in the city is large. It's a 6-bed hospital. It's a caner hospital. It gives excellent care to its patients. It's in a big city, near museums, theaters and restaurants. The salary is high, $1700 a month. But apartment rents are high, too. The hospital in the country is small. It's a 50-bed hospital. It's a general hospital. It takes care of all kinds of patents. It's in a beautiful area, near lakes, rivers and mountains. The salary is average, $1400 a year. But apartment rents are low. Mary likes the city and the country. She doesn't know which hospital to choose. | ||||||||||||||
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