Different countries have different food, such as French fries, Italian pizza and so on. In China, fast food is becoming more and more popular these days. For example, McDonald's and KFC. Why do Chinese people like fast food so much? There are many reasons. First, it is quick. It takes little time. Second, it is easy to carry. Third, people like the restaurant's relaxing environment and American style. Though it tastes good, fast food generally contains little nutrition (营养). If you want to have a healthy body, do not go to fast food restaurants too often. Eat more fruit and vegetables.

开元年间（716—741）政局稳定，经济繁荣、文化昌盛、国力富强的原因不包括（    ）

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