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.

材料一：2015年中国新疆发展论坛于8月18日上午在乌鲁木齐开幕，本届论坛主题为“建设丝绸之路经济带--新疆的发展机遇与选择”。张春赞在开幕式上致辞。他说，今年是自治区成立60周年，今日的新疆经济发展、社会稳定、民族团结、宗教和谐、各族人民安居乐业。悠久的历史、灿烂的文化，现代化的生活在这里完美结合，谱写着神奇的新疆故事。俞正声在贺信上说，作为“丝绸之路经济带”核心区的新疆是中国向西开放的重要窗口，是连接亚欧大陆重要的交通枢纽、商贸物流和科技文化中心。

  材料二：2015年9月30日，中共中央***、***、中央军委主席***在会见来自内蒙古、广西、西藏、宁夏、新疆5个自治区的13名基层民族团结优秀代表时强调：中华民族一家亲，同心共筑中国梦。这是全体中华儿女的共同心愿，也是全国各族人民的共同目标。实现这个心愿和目标，离不开全国各组人民大团结的力量。

请根据上述材料，结合教材，分析回答下列问题：

已知圆的渐开线的参数方程是$\left\{\begin{array}{c}x=\cos \phi +\phi \sin \phi \\ y=\sin \phi -\phi \cos \phi \end{array}\right.$  ( $\phi$ 为参数)则此渐开线对应的基圆的直径是____，当参数$\phi =\frac{\pi }{4}$  时对应的曲线上的点的坐标为____