阅读下列材料，从各题所给的A.B.C.D.四个选项中，选出一个最佳答案。

Dear Jenny,

I am in Beijing, China now, but my parents are in the USA. I live with my broth er Peter. Beijing is big and great. There are many beautiful places and much delicious food here. I like Beijing very much.

    Peter and I are in the same grade, but we are in different classes. We live far from the school and it takes us a long time to go to school. We have to get up at 6:20 in the morning, and then at 6:30 we ride bikes to the bus stop. It takes us about 20 minutes. At about 7:00, we take the bus to school. We get to school at about 7:30.

    We have four classes in the morning and two in the afternoon. I think Chinese is too difficult, but Peter thinks it is easy. He can speak Chinese very well and he often helps me with it.

    How is everything going with you in the USA? Write to me soon.

Love,

Kate

改革是推动社会发展的重要力量和途径。阅读材料，回答问题。
材料一 （秦孝公）有席卷天下、包举宇内、囊括四海之意，并吞八荒之心。当是时，商君（鞅）佐之，内立法度，务耕织，修守战之备；外连衡而斗诸侯。于是秦人拱手而取西河之外。
——贾谊《过秦论》
材料二 如果说从平城到洛阳的北魏是汉化先行者，那么西魏、北周就是追随者。……隋朝的统一，建立在魏晋南北朝民族大融合的基础之上。
——《简明中国读本史》
材料三 在短短的几十年里，日本就按自己的节奏改变了自身。以前它是个前工业时代的封建社会，到19世纪末期，新日本——西方影响和日本传统的混合物……很快将成为西方一个可怕的竞争对手。
——《全球视野下的西方文明史》
材料四 在俄罗斯首都莫斯科红场边有一座塑像，纪念的是曾经解放了千百万农奴、并最终引领俄国抛弃了落后社会制度的改革者。

如图，四边形ABCD中，∠A=135°，∠B=∠D=90°，BC=2$\sqrt{3}$，AD=2，则四边形ABCD的面积是（    ）