Dialects usually develop because a population is isolated from other cultures is well educated sticks to the standard variety avoids jargon

The only one that makes sense is that they are isolated from other cultures. Education does not matter, sticks to the standard variety? If a new dialect was created then they would not stick to another’s dialect, and jargon(slang) is part of someone’s dialect. I hope you can understand this now.

Answer: is c best fits