Santiago, a student, is introduced to smoking cigarettes by his friends. After smoking a cigarette for the first time, he experiences an immense high of nicotine. However, after two months of smoking, he is able to experience the same high only after smoking six cigarettes. Which of the following best explains Santiago's need to smoke an increased number of cigarettes to get the same effect?
A. dopamine dependence
B. revocation
C. withdrawal
D. tolerance