What is role of randomization in experiments mcq question on R programming?

Select all of the true statements about a placebo-controlled randomized comparative experiment.

Observational studies have suggested that vitamin E reduces the risk of heart disease. Careful experiments, however, showed that vitamin E has no effect. According to a commentary in the Journal of the American Medical Association: Vitamin E enters the category of therapies that were promising in epidemiologic and observational studies, but failed to deliver in adequately powered randomized controlled trials. As in other studies, the “healthy user’’ bias must be considered; i.e., the healthy lifestyle behaviors that characterize individuals who care enough about their health to take various supplements are actually responsible for the better health, but this is minimized with the rigorous trial design.

Explain, by describing lurking variables, why observational studies suggest that Vitamin E therapy reduces the risk of heart disease. Note that a randomized controlled trial is a type of experiment.