Tolerance Develops for the Use of Some Drugs Because

 Tolerance develops for the use of some drugs because

A) over time, the blood-brain barrier more effectively blocks the movement of the drug from the blood supply into the brain.
B) more of the drug is absorbed by the body's fat stores, leading to the need to use more to get the same effects.
C) the body's compensation for the drug cancels out its effects.
D) the experienced user's expectations cancel out the drug's effects.