Question 20 is based on the recording you have just heard.

20. What do social workers mainly do?

解析：B。本题目为细节题。问题为：社会工作者的主要工作内容是什么？原文所在句：Its primary mission is to enhance human well-being and help meet the basic needs of all people, with a particular focus on those who are vulnerable, oppressed, and living in poverty.社会工作主要的使命是增强人们的幸福感并且帮助满足所有人基本需求，尤其关注那些弱势的、被压迫的和生活贫困的人。选项B) They help enhance the well-being of the underprivileged（帮助加强社会底层的幸福感），与文中信息一致。本题目出题点位置较明显，在强调处，难点在于原文中出现了长难句。但是其他选项的关键词在文中没有出现，因此干扰性较弱。