The correct answer is:
to show that biodegradable bags do not break down more easily than standard plastic bags.
This option aligns with the purpose of the "What the researchers did" section as it emphasizes the comparative study regarding the effectiveness and environmental impact of biodegradable versus traditional plastic bags. The article discusses concerns about the actual biodegradability of these bags, so highlighting the results of the research reinforces the author's main argument against the assumption that biodegradable plastics are significantly better for the environment.