One of the Differences Between Experimental Research and Correlational Research

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

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