人体内氢随化合物在生物体内代谢转移的过程如图所示，下列分析合理的是（　　）

    Hello! Nice to meet you. Now let me introduce myself (自我介绍) to you. My name is Mary. I'm 12 years old. I'm from Canada and I speak English. I'm a tall girl. I have long brown hair and big blue eyes. I like music a lot. I often sing songs with my friends in my free time. I have a happy family. There are four people in my family. They are my mom, my dad, my sister and me. I like China very much and I want to visit Beijing, but I can't speak Chinese at all.

    I hope (希望) to be your friend, then we can help each other with English and Chinese.

根据材料内容，选择最佳答案。

如图，在正五边形ABCDE中，连接AC、AD、CE，CE交AD于点F，连接BF，已知AB=1，则DF的长是（　　）