A study showed that people who take a B12 vitamin daily have a significantly better chance of protecting against Alzheimer's dis
ease than those who did not take the vitamin daily. Which of the following statements is/are correct? I. This study provides evidence that taking a B12 vitamin daily contributes to protecting against Alzheimer's disease.
II. The general health consciousness of people who take B12 vitamins could be a confounding variable.
III. This is an observational study and not an experiment.
a. l only
b. III only
c. l and II only
d. ll and III only
e. I, II, and III
