EXPLANATION

Question "c" is the best choice. You might be asking, "How can I research something whose effect hasn't yet been felt?" You can logically posit what "might happen" in the future based on what "has happened" in the past. For example, your research may bring you to the major things thought to have caused obesity in the recent past (last 2-3 decades) in order to establish a direct relationship between cause and treatment. Once you establish that direct cause-and-effect relationship, you can project similar types of relationships based on the new genetic research.