What evidence from the video indicates that the rats, like humans, find nicotine to be a weak reinforcer?
a. the rats work much harder after ingesting nicotine.
b. the rats press the lever least when cocaine is presented.
c. the rats would rather work for drugs other than nicotine.
d. the rats press the lever more often to ingest nicotine.

b. The rats press the lever least when cocaine is presented.

Explanation:

   Reinforcement or reward refers to the physiological processes by which a given behavior, such as drug use, becomes habitual.  This  occurs when neurons release the neurotransmitter  dopamine to the nucleus accumbens (NAc) after drug use.

  In tobacco, nicotine is the main component  triggering of the reinforcement. Once inside the brain,  nicotine activates nicotinic receptors, which in turn  contributes to the reinforcement mechanism. Following repeated exposure to nicotine, a neuroadaptation process is established for some (but  not all) effects of nicotine. Increased brain nAChRs (acetylcoline receptors) are observed in response to desensitization of these nicotine-mediated receptors.  This desensitization can play an important role in the development of tolerance and dependence.

  The fact that nicotine is a weak reinforcer, means that maybe the rat already had an neuroadaptation with this drug, not feeling anything with this drug anymore, and thats why he would prefer other drug, like cocaine, pressing the lever of nicotine less often.

answer; training;