The correct answer is A. The habit of talking drugs has been growing within the urban youth.
The other options are incorrect because they do not make sense in the context of the sentence. Option B, “in,” is incorrect because it would imply that the habit of talking drugs is located in the urban youth. Option C, “from,” is incorrect because it would imply that the habit of talking drugs is coming from the urban youth. Option D, “upon,” is incorrect because it would imply that the habit of talking drugs is acting on the urban youth.
The sentence is about the increase in the number of urban youth who are talking drugs. The word “within” indicates that the increase is happening within the group of urban youth. This is the most logical interpretation of the sentence.