Constancy of conditions is often enhanced through: a. Maximizing the internal validity of the study b. Using a crossover design c. Avoiding contamination of treatments d. Having standard written research protocols

Answer: Option (d) is correct

Explanation:

Constancy of condition is the process in which a variable and its aspects are kept constant in a study so that its impact is persistent throughout the research. It can be improved through research protocols that are written as per standards so that more consistency and reliability can be established in study.

Other options are incorrect because increasing internal validity, cross-over design utilization and keeping away treatment contamination and the mechanisms for improving constancy of condition. Thus, the correct option is option (d).