C-None of these are found in an observational study
Explanation:
(A.) controlled variables are a part of what's found in a controlled experiment. (B.) manipulated variables are a part of what's found in a controlled experiment. (C.) Answer choice A. or Controlled variables, Answer choice B. or Manipulated variables, and Answer choice D. or Control groups are a part of what's found in a controlled experiment. (D.) Control groups are a part of what's found in a controlled experiment. Therefor this only leaves one answer and that answer is Like I said C-None of these are found in an observational study.
