阅读下面短文，从短文后所给的A、B、C、D四个选项中选出能填入相应空白处的最佳选项。

    This is an apple tree. There are many 1 on the tree. There are some 2under it, too. They are 3 happily. Under the tree I can 4 a boy and a girl. They're playing games with the dogs.  The boy is 5 a blue sweater and white shoes. He is Jim. He is 6 American student. He is 14. He 7 his school very much. The girl is Jim's sister, 8 name is Cindy. She is 11. She is in a yellow dress. Her shoes are yellow. 9 . Now they are standing here, they are waiting for their friends. They 10 to play games under the tree.

观看视频CO还原CuO的实验，思考交流以下问题：

下列属于今天青藏牧区的生活变化的有  (    )

①有的牧区建起了定居点      ②牧区在水利建设方面有了改进  

③改进了牧区的围栏建设       ④畜牧业产品大多在本地销售