Each of the Following Bolsters Confidence in the Obtained Results

Each of the following bolsters confidence in the obtained results of an experiment, EXCEPT:

A) when researchers find a significant difference between the control and experimental groups on the manipulation check.
B) the investigation reveals a significant difference between groups on preexisting differences.
C) statistical analyses reveal a moderate effect size.
D) the investigation fails to reveal significant differences between groups on preexisting characteristics.