统一是中国历史的主流。历史学家田余庆教授在论文《中国古代史上的国家统一问题》中对中国历史上的三个统一时期进行了系统的论述。文章的第一部分阐述了国土开发和国家统一的关系。阅读以下相关摘要：
材料一  统一的第一个时期，大体上是西周到秦。西周有一个中央政权，在中国北方黄河流域的范围之内发号施令，让自己的功臣、周室宗亲等等各种各样的人到东方去开辟土地。与周代的制度相比，秦汉所形成的统一否定了周的这个政治制度，但是又不是绝对否定。
材料二 秦汉以后到元是第二个阶段，这个时候中国北方，东部和西部结合在一起，要开发的地区是广大的中国南方。秦统一以后，对开发国土做过一件大事，就是迁徙50万身份低下的或犯了罪的人，到岭南去戍守，把中国南方的国土一直推进到南海边上。这对中国以后逐步开发南方起了很大作用。当然，南方处在落后状态，又有很多民族存在，跟北方交融不那么容易完成。历史为此付出了1000多年的时间。
材料三 到了元以后，中国的统一，从地域方面来说进入了第三个时期，理当是开发大西部。元以后，实际上在东部的南北，没有再出现分裂的可能性，问题在于西部。但是元以后中国缺少开发的条件，广大的西部长期处在一个待开发的落后状态。我们今天开发西部是对于中国统一的进一步巩固开启一个新的起点。美国在1 9世纪开发西部，以至于西部和东部走向平衡，维持了美国今天的国情局面。
 

阅读下面材料，从A、B、C、D四个选项中选出一个最佳选项。

    Car-hailing company DiDi signed an agreement with TAL Education Group to provide free online courses for the children of taxi drivers. The courses, worth 30 million yuan, cover all subjects from primary to high school. Children can study courses at home, saving parents' time to spend or pick up children from off-line after-school classes.

    According to Zhu Jingshi, vice president of DiDi, all 153 million registered (注册) taxi drivers of DiDi can ask for the courses on the company's mobile app. The car-hailing company will evaluate (评价) the drivers and provide courses on the basis of the time they became registered drivers with the company, the number of passengers served and evaluation from passengers.

    The health and education of children have remained top priorities of Chinese parents, including taxi drivers. A survey done by DiDi and TAL showed that although the average monthly income (平均月收入) of taxi drivers is only 6000 yuan, many would like to pay 40 percent of their income for their children's education.

    The survey found that most taxi drivers were born in the 1970s and 1980s and worked seven days a week. More than 70 percent of them have children under 18 but very few have time to be with family and children. Only 8 percent of them said they had guided their children in doing homework. Because of these, 60 percent of drivers hope their children could receive the guidance from professional services.