在△ABC中，AB=BC，∠ABC=84°，BD是∠ABC的平分线，DE∥BC；求∠EDB的度数

制造航空飞行器时，为了减轻其质量，采用的材料应具有的特点是（　　）

    It is Saturday morning. The sky is blue. My father and I are going to the park. There are a lot of people in the park. Some children are running on the grass. A dog is running after them. Some men are sitting on the grass. They are talking. Two girls are flying a nice kite. Three women are standing under a tree, and they are watching the children playing. There is a boat in the lake and two women are boating. Everyone in the park is very happy.

①性激素  ②血红蛋白  ③抗体  ④淀粉  ⑤纤维素  ⑥脂肪酶  ⑦氨基酸．

预防不良行为，矫正严重不良行为，对青少年而言，更重要的是（ ）