Final answer:
A standard randomised controlled trial (RCT) is the best design option to maximize the exchangeability of groups being compared to assess causality between an exposure and a disease. It minimizes confounding variables through random assignment and often includes blinding to prevent bias.
Step-by-step explanation:
In assessing whether a given exposure causes a particular disease, the most effective design to maximize the exchangeability of groups being compared is b) A standard randomised controlled trial (RCT). An RCT involves randomly assigning subjects to either a treatment or control group, thus minimizing the presence of confounding variables. This is because randomization ensures that each participant has an equal chance of being assigned to either group, hence any differences in outcome between the groups can more confidently be attributed to the treatment itself rather than to other factors.
Additionally, an RCT often includes blinding, where neither the participants nor the researchers know who is receiving the treatment and who is receiving the placebo. This further ensures that the results are not biased by the expectations of either the participants or the researchers.