在△ABC中，点D、E分别是边AB、AC上的点，且有$\frac{AD}{DB}$=$\frac{AE}{EC}$=$\frac{1}{2}$，BC=18，那么DE的值为（　　）

治理水土流失的工程措施有（　　）

①修水库②平整土地③植树造林④修水平梯田⑤深耕改土

    It is Saturday morning. Mrs. Black and her daughter Kate go to the bookshop near their house. Mrs. Black wants to buy some picture books for her grandson. Kate wants to buy some storybooks. In the bookshop Kate meets her old classmate, Sue. They are good friends. They talk and talk for a long time and forge to buy books. At twelve o'clock Mrs. Black finds them and asks Sue to go and have lunch in their house, Sue says: “Yes.” The two girls are very happy.

读图，回答以下问题。