How did the Grants test their hypothesis that differences in the finch songs can keep different species of finches from breeding with one another

Which of the following initial observations would more directly lead to this research study? a) ginko biloba is cost effective and also possesses heart-protective, antioxidant, anti-inflammatory properties. b) metformin is an effective treatment of patients with t2d, but shows side effects that complicate the disease state. c) over the past several years, the cost of treating t2d within the united states has increased dramatically. d) many plants contain molecules that improve the health and quality of life of patients with a variety of diseases like t2d. e) t2d affects millions of individuals in the usa and worldwide many of who could benefit from improved therapies.