The brain is susceptible to addiction largely because of its response when dopamine levels are high. this response primarily involves a. reducing dopamine receptors. b. producing more serotonin when dopamine levels are high. c. increasing dopamine receptors. d. producing more dopamine when induced by drugs.

A

Explanation:

Dopamine release in the brain causes  a pleasurable feeling. This system is utilized by the reward center in the brain significant in  encouraging life-sustaining behaviors such as satiety. However, drugs artificially induce this region of the brain causing the subject to alter their mood. Drugs induce a higher amount of dopamine release than reward centers of the brain. The brain adjusts by reducing the number of dopamine receptors as it tries to gain homeostasis. However, this can result in addition because one steadily requires more drugs to induce the same dopamine effect. The subject, therefore, steadily becomes tolerant of the number of drugs he was taking and needs to increase the intake.

i think the answer is a.keratin is the pigment responsible for skin color.