DrLand Conducted a Study in a Preschool to Test His

Dr.Land conducted a study in a preschool to test his hypothesis that the amount of unstructured time (free play) in a day affects the amount of unruliness that children display.Teachers systematically varied the amount of free play each day for a month,and Dr.Land's research assistants recorded the amount of unruliness children displayed each day.This study would best be described as a(n)

A) correlational study.
B) laboratory experiment.
C) field experiment.
D) quasi-experiment.