The best source for his research about the mechanism of the drug would be : A peer-reviewed research article in a scientific journal ( A )
A peer-reviewed research article would be a best source for his research because peer-reviewed articles are written and reviewed by colleagues in the same scientific field of study.
An article written by an author about how a drug will alleviate pain in dogs and cats and reviewed by his peers will contain detailed information on the mechanism of such drug, therefore this article will be very informative and helpful to the student.
Hence we can conclude that , The best source for his research about the mechanism of the drug would be A peer-reviewed research article in a scientific journal.
