Hello! My name is Mike. I am from the USA. Now I am in China with my parents. I like China. I like Chinese food, too. I have breakfast at home. I eat an egg, bread and porridge(粥)for breakfast. I do not like milk. I have no time to go home for lunch. So I have it at school. The lunch in our school is good. I can have different food for lunch. I eat rice, meat and vegetables. Sometimes I have noodles（面条） and dumplings(饺子). I have dinner at home with my parents. Sometimes we go out to eat with friends. We have chicken, vegetables and fruit.

如图，在等腰Rt△OAA₁中，∠OAA₁=90°，OA=1，以OA₁为直角边作等腰Rt△OA₁A₂，以OA₂为直角边作等腰Rt△OA₂A₃，…则OA₄的长度为____．