Nicotine causes the brain to release chemicals that make you feel pleasure but overtime you may need more and more nicotine to get the same effects can eventually lead to nicotine addiction which can lead to affects that cause decreased appetite heighten mood increase heart rate and blood pressure nausea diarrhea and increased alertness.
The answer to your first question is D. Three months. The reason why is it takes at least 3 months to have detectible HIV antibodies. In rare cases, it may take up to 6-12 months.
The second question I'm not 100% positive on but I believe the answer would be B.