Which is NOT mentioned in the passage as the reason for Americans feeling of loneliness？A．

Which is NOT mentioned in the passage as the reason for Americans feeling of loneliness？

A．People find it more difficult to establish more social relationships as becoming older and older.

B．The increasing mobility of American society nowadays.

C．Certain situational factors may bring about the feeling of loneliness.

D．People inherit loneliness genetically and feel long-term emptiness and isolation.

请帮忙给出正确答案和分析，谢谢！