Which of the Following Is a Principle Derived from the Observation

Which of the following is a principle derived from the observation that heroin is more addictive than morphine?

A) Food is a poor reinforcer for hungry rats.
B) Immediate reinforcement is more important than quantity of reinforcer.
C) Quantity of reinforcement is more important than immediacy of reinforcement.
D) Longer delays between response and food delivery results in faster learning.
E) Drugs that are rapidly cleared from the brain are more addictive.