如图,在梯形ABCD中,AD∥EF∥BC,BE=3AE,AD=3,EF=4,则BC=____.

    A new study says that American children have exciting after-school life. Many junior and senior students have a lot of interesting things to do in their free time. About 57% students have activities every day. 82% students have activities at least four times a week. American students spend their free time doing sports or enjoying arts, music and dancing. They like to have fun outside school because they can make a lot of friends during their activities.