One of the Essential Differences Between Experimental Research and Correlational

Multiple Choice

One of the essential differences between experimental research and correlational research is that:

A) in experimental research all variables are measured,while in correlational research at least one variable is manipulated.
B) in correlational research all variables are measured,while in experimental research at least one variable is manipulated.
C) experimental research tends to use random sampling,while correlational research tends to use random assignment.
D) experimental research tends to have higher external validity than correlational research.