<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:The study is performed to examine the association between type 2 diabetes mellitus DM2 and Alzheimers disease AD. Group of 250 subjects diagnosed with DM2 and a matched group of 250 subjects without DM2 are enrolled. Each subject is monitored regularly over their lifetime for the development of symptoms of dementia or mild cognitive impairment. If symptoms are present, an autopsy is performed after the patients death to confirm the diagnosis of AD. Which of the following is most correct regarding this study?? A: It is a retrospective observational study., B: It can provide proof of causation between DM2 and AD., C: Relative risk cannot be determined from this study., D: It is a prospective observational study., E: It is a case-control study.,  <response>: This is a prospective observational cohort study. The question describes following two matched groups of subjects over time to assess the outcome of interest, which is development of Alzheimers disease. It is not a retrospective study because it follows subjects forward in time. It cannot provide definitive proof of causation between diabetes and Alzheimers, only an association. Relative risk can be calculated by comparing the incidence of Alzheimers in the diabetes group versus the control group. It is not a case-control study because subjects are not selected based on presence or absence of the outcome of interest Alzheimers disease.D: It is a prospective observational study. 