What is the primary reason that descriptive and correlational research cannot determine conclusively that variables have a cause-and-effect relationship

A)  The researcher observes behaviour under artificial situations. 
B)  The data collected frequently comes from direct observations or statements made by subjects. 
C)  Only an experimental group is used. 
D)  The researcher cannot control events or manipulate variables.

Descriptive

Pertaining to the detailed description of characteristics, behaviors, or the setting of an event without imposing any interpretations or judgments.

Correlational Research

A method of research that examines the relationship between two or more variables to determine if a change in one is associated with a change in the other(s).

Cause-and-Effect Relationship

A connection between two events where one is the result of the other or others.