今年，我市发现人感染H7N9禽流感病例，该病是由H7N9禽流感病毒引起的，它通常只感染鸟类，少见情况会感染人、猪、马等哺乳动物．专家介绍说：“对于所有的流感，我们都建议两条预防原则：两勤三早．”“两勤”就是勤洗手、勤通风，“三早”就是早发现、早诊断、早隔离治疗．根据上述资料，请回答：

阅读理解：读A篇短文，根据短文内容选择最佳答案。

    Do you like Pleasant Goat and Big Big Wolf? It's an interesting cartoon movie. Do you want to know what they do in their village every day?

    I'm Nuan Yangyang. On school days, I always go to school at 8:00 in the morning. Then I go home at four fifteen in the afternoon. Then I do my homework at 5:00 in the afternoon. I have no homework on weekends.

    I'm Fei Yangyang. I want to be healthy, so I always get up at six o'clock in the morning. And I run to a sports club to play sports at 8:15 in the morning. Then I play games with my friends and get home at three o'clock in the afternoon.

I'm Lan Yangyang. I love eating and sleeping. And I don't like doing sports. I have meals at home but I never wash the dishes.

    I'm Mei Yangyang. I am a pretty girl. I like going to clothes stores. The clothes there are nice, so I often buy nice skirts there. I go to a singing club on weekends.

    I'm Xi Yangyang. I like helping others. So I usually take the bus to the English club at ten thirteen in the morning. There I help two kids learn to speak English.

在1：500000的地图上，实地距离为20千米的两城市在图上的距离是（　　）