Option A supports the idea that loneliness is a prevalent problem.
The detail from the text that underscores the prevalence of loneliness is found in option A: "Wealthy but alone, this once vivacious, social man no longer knew his neighbors and had lost touch with his former co-workers" (Paragraph 2). This statement highlights the experience of a wealthy individual who, despite financial success, grapples with loneliness, indicating that loneliness is not exclusive to any particular socioeconomic group.
The other options provide relevant information about loneliness but do not directly convey its prevalence. Option B discusses the inclusivity of loneliness across different demographics, acknowledging that it affects introverts and extroverts, rich and poor, and various age groups. Option C addresses the importance of choosing positive online interactions but does not explicitly discuss the prevalence of loneliness. Option D shares a personal experience of receiving support during tough times but does not provide broader evidence of the widespread nature of loneliness in society. Therefore, option A is the most direct and specific in supporting the idea that loneliness is a prevalent problem.