<span>This research study would be a prospective cohort study. </span>
<span>In this study, the groups are different in some way, for example, a control group which received no treatment, a standard group who received a well-studied drug and a test group who received a new drug. These groups are followed over time and the outcome (such as curing a disease or alleviating symptoms) will be compared. </span>
I believe it would be B. More than a year (Since it is a slow change, and that is the longest amount of time). Hopefully this helps
