Which statement accurately describes the relationship between the brain and addiction?

a. all drugs act on dopamine synapses in the same way.
b. normal activities produce heightened responses once receptors are reduced.
c. the brain reacts to excessive dopamine levels by increasing the number of dopamine receptors.
d. a higher amount of addictive chemicals are needed to get the same high when fewer receptors are present

i just took the test the answer is "d"