Answer:
Counterbalancing.
Step-by-step explanation:
In experiments, counterbalancing is the process that helps the researcher to control the effects of nuisance variables. Nuisance variables in the research are the variables that are unwanted and are of no value to the researchers.
Counterbalancing helps the researcher to make certain changes in the experiment by changing the ways of treatments to different participants in the group.
In the given case, Eric can fix the problem with order effect by counterbalancing, which will help Eric to eliminate unwanted variables from the experiment and change the ways of treatment to different participants.
So, the correct answer is Counterbalancing.