What's the Difference Between an Experiment and a Correlational Study

What's the difference between an experiment and a correlational study?

A) Psychologists manipulate and measure variables in experiments but only measure variables in correlational studies.
B) Psychologists use random selection in experiments and random assignment in correlational studies.
C) Psychologists pay participants in experiments but do not pay participants in correlational studies.
D) Psychologists must secure IRB approval for experiments but not correlational studies.