Which Statement Describes the BIGGEST Limitation of Correlational Research

Which statement describes the BIGGEST limitation of correlational research?

A) It does not allow conclusions about cause-and-effect relationships.
B) Its results can be applied to only one subject at a time.
C) Relationships between variables are inconsistent, so findings cannot be applied to the real world.
D) The manipulation of a correlational variable requires an ABAB design, which is not always practical.