题干

国产大型客机C919于2017年5月5日在上海浦东国际机场首飞成功。C919大型客机的研制,使用了大量的铝锂合金、钛合金和复合材料等。下列有关说法错误的是(   )

A:锂的密度应该比较小

B:金属铝质轻、耐腐蚀、延展性好

C:铝锂合金属于复合材料

D:钛合金是以钛为基础加入其他元素熔合而成的

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C

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    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.