The giraffe is the tallest modern land animal. It can be over 5. 5 meters tall. Its neck alone may be 1. 9 meters long. Yet the giraffe has only seven bones in its neck, the same number as in the humans'. Even a small bird has many more bones in its neck than a tall giraffe. Each bone in a giraffe's neck is very long, while the bones in a human's neck are short. That makes the difference. A female giraffe gives birth to one baby at a time. The baby, called a calf, is about 1. 9 meters tall at birth. By the age of eight it is full-grown. The giraffe eats mostly leaves. Because it has a long neck, it can reach the high leaves on the trees.

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如图，四边形ABCD是平行四边形，点E在CD上，连接AE交BD于点F，则下列结论错误的是（　　）

下列观点中，符合权利和义务相统一的是（　）

已知：如图，AD、BE分别是△ABC的中线和角平分线，AD⊥BE，AD=BE=6，则AC的长等于____ .