The answer is A: a university site showing the results of a study on which foods absorb chemicals.
The source of option A provides the most reliable information for Jena's research because the university site is not only presenting an opinion or suggestion about the subject, but it is showing the results of a study about the relation of the chemicals, the foods and absorbency conditions etc. A blog, a wiki and a website will probably have to use the same information in order to write their articles.