题目

It was Mary's birthday. She received a letter from her uncle. “Dear Mary,” he wrote in his letter. “Happy birthday! I'm sending you some chickens. They will arrive tomorrow. I hope you'll like them. Uncle Toby.” Mary was very pleased. She liked eating eggs and chicken. “I can keep the chickens for their eggs or eat them,” she thought.When the chickens arrived the next day, they were put in a box. Mary was very happy. She took the box off the truck and began to carry it into her garden，but the box of the chickens was so heavy that she dropped it. The box fell on the ground and bro如图，直角梯形ABCD中，∠A=90°，∠B=45°，底边AB=5，高AD=3,点E由B沿折线BCD向点D移动，EM⊥AB于M，EN⊥AD于N，设BM=x，矩形AMEN的面积为y,那么y与x之间的函数关系的图像大致是（    ）