Observational studies involve researchers analyzing data through observation, without intervention.
- Case-control study: A retrospective design comparing individuals with a condition (cases) to those without (controls).
- Cohort study: A longitudinal design tracking a group (cohort) over time to evaluate outcome development related to exposures.
- Randomised Controlled Trial (RCT): An interventional study with participants randomly assigned to groups.
- Non-randomised Trial: An interventional, non-observational study, despite lacking randomization.
Therefore, (A) and (B) only is the correct answer.