教材中“整式的加减”一章的知识结构如图所示，则A和B分别代表的是（　　）

①践行社会主义核心价值观            ②消除家庭成员意见分歧

③加强社会主义精神文明建设          ④弘扬中华民族的传统美德

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     A dog is walking along a road. It is a big dog. It is carrying a piece of meat. The piece of meat is in the dog's mouth. The dog is walking across a bridge now.There is water under the bridge. The water is very deep. The dog is looking into the water. It can see a dog in the water. This dog has a piece of meat in its mouth, too. The big dog is barking at the dog in the water. It wants its piece of meat, too. The big dog's piece of meat is falling into the water.