题目

Deciding which English-speaking country to study in wasn’t difficult for Ann; She had always wanted to visit America. “I wanted to study in an  English-language country and I always wanted to visit America because it always seemed to me a very beautiful and friendly country.” Ann is more than happy with the quality of the education she is receiving in America, particularly with the subjects and strong academic support.“ I am very happy with the quality of education I am receiving. All my subjects are useful and connected. I am happy with help I receive from the lecturers and tu如图，点D、E分别是△ABC中AB、AC边的中点，已知DE=3，则BC= ．