If Physical Control,randomization,and Design Features Do Not Eliminate the Differential

Multiple Choice

If physical control,randomization,and design features do not eliminate the differential effects of extraneous variables among treatment groups,the experiment

A) has been confounded, but causal statements are still possible
B) has been confounded, and no causal statements are possible
C) must be repeated without the presence of extraneous variables
D) loses external validity, but can still salvage internal validity