以下物质在空气中不会发生自燃的是（　　）

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   Every country has its own way of cooking. American people have their way of cooking, don’t they?
   Most people in the United States like fast food, but if you think that American people don’t like cooking, you are wrong. It’s true that most Americans eat fast food for their breakfast and lunch, but they also think cooking is interesting. Parents see the importance of teaching their children how to cook, and most Americans say that home cooked meals are the best.
   Americans have their own way of cooking. For example, baking  (烘烤) is the most popular way of cooking in America. Most American families have ovens. American cooks pay attention to (注意) the balance of food. In planning a big meal, they try to cook meat, a few vegetables, some bread and often some sweet food. They also like to make the meal look beautiful. There are many kinds of food of different colors, so the meal is healthy and looks beautiful, too.

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黄土高原是中国四大高原之一，也是中华民族古代文明的发祥地之一，是地球上分布最集中且面积最大的黄土区。图8-1为黄土高原位置和年降水量分布示意图。