Question

2、 the author makes clear that research on the positive effects of fermented foods on human health is fairly new. difficult. expensive.

Explanation:

To solve this, we analyze the context (implied from the question about research on fermented foods' health effects). Typically, research on such topics (fermented foods and health) is often described as "fairly new" in many academic or informational texts, as the field of studying probiotics and fermented foods' health impacts has gained more attention relatively recently. "Difficult" and "expensive" are less likely as primary descriptions for this type of research in general contexts without specific cues about challenges or costs.

Answer:

A. fairly new.