The Factor That Makes the Data from True Experimental Designs

The factor that makes the data from true experimental designs more valid than data from any pre-experimental designs is

A) matching.
B) randomization.
C) the absence of extraneous sources of error.
D) the fact that the results can always be generalized to the larger population.
E) the fact that each of the test units is measured before and after the introduction of the experimental stimulus.