[解析]
(1)细节理解题。根据第二段They measured people's attitudes and feelings before and after watching social media sites.They found that the mere time people spent on social media,the more unhappy they became.(他们测量了人们在观看社交媒体网站前后的态度和感受。他们发现,人们花在社交媒体上的时间越长,他们就越不开心。)可知,如果人们过度使用社交媒体,人们会不快乐。故选B。
(2)推理判断题。根据第三段The number of "likes" and comments on their posts can make them anxious about their popularity.Of course,there is also the problem of "cyber bullying" where people become victims of bullying online when others make negative or cruel comments about them.(他们帖子上的"点赞"和评论数量会让他们对自己的受欢迎程度感到焦虑。当然,还有"网络欺凌"的问题,当其他人对他们发表负面或残酷的评论时,人们会成为网络欺凌的受害者。)可知,发布积极故事的人们也会害怕遭遇其他人的网络欺凌。故选C。
(3)推理判断题。根据第三段There are a number of reasons for this.(这个的原因有很多。)可知,本段主要介绍了人们使用社交媒体时间越长越不开心的原因,即作者是通过给出原因来展开第三段的。故选A。
(4)写作目的题。根据最后一段This research shows us that it is important to find a balance between our online and offline lives.We don't have to disconnect from the Internet to live a happy life,but we should realize that the pictures we see and stories we read are only part of a bigger picture.(这项研究向我们表明,在我们的线上和线下生活之间找到平衡是很重要的。我们不必为了过上幸福的生活而与互联网断开连接,但我们应该意识到,我们看到的图片和读到的故事只是更大图景的一部分。)可知,作者写这篇文章是为了提醒读者平衡线上和线下生活,这是很重要的。故选D。