Dr. johansen randomly assigned research participants to three different groups during her last experiment. she then proceeded to give all the participants in the experiment a new study technique designed to enhance their learning for the upcoming test. what critical error did she make during her experiment?

She did not create a control group for this test. There wasn't a group that had no treatment (or study technique, in this case). By giving each group a new technique and a fourth group no technique at all before measuring their learning, Dr. Johansen will not be able to credibly say if any of the techniques increased the subjects' learning potential.

The answer is the third one or c

Ithink the answer you are looking for is (b).