Answer:
The answer is D. Correlational design.
Explanation:
Correlational designs seek to study the relationship between two or more variables in a piece of research. For example, a news article called "Students with healthy diets get better grades at school" is probably based in a correlational study.
It's important to recognise that correlation is not the same as causation. This means: even if two variables appear to be related, that does not indicate a direct cause-effect relationship.