题目

Organic farmers also use many other methods to produce rich soil. They often change the kind of crop grown in each field every year. For instance, they may grow corn or wheat in a field one year, and then grow beans there the next. Why different crops are grown is because they put important minerals back into the ground, making it ready for the next batch of crops. Organic farmers also plant diverse crops that use different depths of soil to help keep it rich. For example peanuts grow on the ground’s surface, but many other vegetables put down deep roots. The goal of using different 在北方的冬季，常见的几种物态变化现象中，属于凝华的是（　　）A．室外冻冰的衣服变干B．房间窗户玻璃的内表面出现冰花C．湖面结了厚厚的一层冰D．正在跑步的人，口中呼出“白气”