A) When researchers inadvertently create a flaw in their experiment that is a threat to internal validity, it is known as a .
B) If these flaws coincide with the experimental manipulation and call into question whether or not the manipulation or the flaws affected the dependent variable, this is known as .
C) Whereas, if the flawed part of the experiment does not coincide with a specific group, and is introduced at random, this is known as and does not necessarily pose a threat to internal validity.