Question 21 is based on the passage you have just heard.

听力原文

        Despite smartphones and social media, young people today are as socially competent as those from the previous generation. At least, this is what a new study suggests. For the study, researchers compared teacher and parent evaluations of American children who started kindergarten in 1998 with those who began school in 2010. The former group entered kindergarten when mobile phones were luxuries. The latter group started school when mobile devices were widespread. (19) [Results showed both groups of children were rated similarly on important social skills.] These included the ability to form and maintain friendships and get along with people who are different. They were also rated similarly on self-control, such as the ability to regulate their temper. In virtually every comparison made, ratings of social skills either remain constant or improved for the children born later. There was one exception: (20) [social skills were slightly lower for children who accessed online games and social networking sites many times a day.] (21) [Adults are worried when technological change starts to undermine traditional relationships, particularly the parent-child relationship.] The introduction of telephones, automobiles and radio all led to moral panic among adults of the time, because the technology allow children to enjoy more freedom. Fears over screen-based technology represent the most recent panic in response to technological change. But overall, the study found little evidence that time spent on screens was hurting social skills for most children.

21. What is adults’ worry about technological change?（成年人对于技术变革有何担忧？）

解析：C。录音中提到，当技术变革开始破坏传统关系，尤其是亲子关系时，成年人感到了担忧。由此可知，技术变革可能会损害亲子关系，C项与此内容相符，其中的hurt对应录音中的undermine，their relations with children是对录音中the parent-child relationship的同义替换，故C项为正确答案。

错项排除：录音中没有提到技术变革会威胁到孩子们的安全，故排除A项。录音中只提到技术变革可能会破坏传统关系（traditional relationships）、引起成年人的道德恐慌（moral panic），并没有提到技术变革对价值观的影响，故排除B项和D项。