Which factors of her study can Tasha control to ensure it closely resembles the original study?

The number of subjects in Tasha's study is a critical factor she can control to ensure her study closely resembles the original study. Controlling the sample size helps in maintaining the statistical power of the study, allowing for more reliable and valid results. A similar number of participants can also help in comparing outcomes more effectively against the original study, particularly if the original had a specific sample size that contributed to its findings.

While other factors, such as the lifestyle and physical condition of the subjects, genetic variances, and age and sex, have important implications for the study, they are less directly controllable. For example, while Tasha can select participants within certain age and sex ranges, individual genetic makeups and the personal lifestyle choices of subjects are inherently variable and may not be easily standardized. Thus, controlling the number of subjects is the most feasible way to mimic the original study’s conditions.