In answer to your doubts about #D - there is a mention of popularity, though I think it is stretching the interpretation a little :Back in the early 1990s, when was rap was beginning to be popular,
In answer to your objection to #C - I think the inference is taken from para.1 where gang warfare is specifically referred to.
Also, is the following sentence correct:
“All rap music is doing to show how horrible and inhuman life is in the ghettos across the country.”
It seems like really odd to me, especially the part in bold. I rather agree - I think "is" has been missed out in front of "to show".
I don't think the writer (who is not a good one, by the way) is saying that rap is the reason for the gang warfare, but that in rap can be identified the reasons.
The whole thing is just really confusing. Are the gang members fighting because they represent either East Coast or West Coast or do they just fight for different reasons and just happen to listen to rap music? Or does rap music influences the rap members to be more violent which leads to violence?
It seems to me that preference for West/East Coast rap is an expression of a gang's internal loyalties, and that the violence, the use of/liking for rap, and the actions of gangs in the ghettoes are interlinked and mutually connected.
The passage looks as if it has been taken from a (not very well) written piece of journalism. I am not surprised you have found it confusing.