Answer:
C. Heredity
Step-by-step explanation:
We usually look up to people that are involved in our lives.
His parents had history of smoking, even though they're non smokers now. He probably grew up to the smell of tobacco and he was surrounded by the group of smokers which could've resulted in him being a smoker, too.
He has an idol who is a non-smoker, but some other kids look up to celebrities that promote poor lifestyles and bad habits.
It's the same when it comes to our friends as they are people who we spend most of our times with. If they start smoking or consuming alcohol, we are very likely to do it too. Not everyone has a strong opinion about certain things as there are many unstable teenagers.