如图，⊙O是⊿ABC的外接圆，已知AD平分∠BAC交⊙O于点D，AD=5，BD=2，则DE的长为（   ）

    London is the capital of England. It is a very big____(城市). There are____(三) beautiful parks in London. And there is a zoo in one of the parks. The zoo is____(很棒的) . There are many animals from Africa,____（亚洲），America and Europe in the zoo. At____(周末) , we can see lots of people in the parks. Some children like to play football or take____（照片）. Some like to listen to____（音乐）or talk with friends. Their parents can read books on the chair or____（散步，步行）near the river. Look! Over there! Some girls____（跳舞）and two birds are singing for them . Some boys are playing the guitar near the____（高的）tree. Everyone is happy.