Answer: A- Design confound
Explanation:
A design confound is method in an experiment that creates an extra variable that was not accounted for which can ruin an experiment and give you wrong results by suggesting correlation or creating a bias. This threatens internal validity due to its relationship with the dependent and independent variables, because it suggests that the study is not testing for what it should test for.
it is very necessary to identify one and avoid them to avoid disrupting an experiment
Dr gong in this case finding out the air conditioning had been turned off during experiment when it needed to be on during the collection (ie one variable has been challenged) has given her a threat to internal validity of her results in the experiment.