Which of the following would be most relevant to a research paper discussing the negative health effects of soft drinks?
-interviews with the author's personal physician
-list of options for beverages that could be sold in vending machines
-studies showing a connection between higher consumption of soft drinks and health problems
-testimony from various people who drink soft drinks regularly and are healthy

The answer is C: Studies showing a connection between higher consumption of soft drinks and health problems.

If the hypothesis of the writer is that the consumption of soft drinks has negative health effects, then he has to make an argument based on demonstrable proofs, such as the use of findings from other studies that show a correlation between soft drinks and negative health effects. Personal testimonies, marketing options, or an appeal to an authority figure would not be enough to make a strong argument since the writer´s statements could not be tested or replicated, which is the essence of scientific argumentation and research in general.