I wonder if any of my old friends remember being my friend . i do nt really talk to anyone from the city anymore . but we used to have so much fun .

Pick from:
[a]. None of the above choices .;
[b]. They are sad over their place in the city .;
[c]. They are sad over living in the city .;
[d]. They are sad over their friendships .;
Answer the following question: What is causing the narrator to feel depression ?
[d].