Fred's Advisor Noticed That He Had Not Included the Same

Multiple Choice

Fred's advisor noticed that he had not included the same words in each list used to test whether the color of ink affects memory.This meant the lists differed in both content and ink color.Fred won't be able to easily interpret his results because:

A) reactivity has occurred
B) his data have poor external validity
C) his experiment included a confounding variable
D) he did not use a control group