Final answer:
A well-designed study with random assignment and control for lurking variables minimizes threats to internal validity, hence none of the options listed would be a threat if these measures are taken.
Step-by-step explanation:
The question addresses threats to internal validity in a comparative analysis. Internal validity refers to the extent to which a study can demonstrate that a cause-and-effect relationship exists between the treatment and the outcome. Potential threats include multi treatment interference, where multiple treatments affect the results; non-reversibility of effects, where effects from an earlier treatment cannot be reversed; and incorrect attribution of the effect to only one treatment, where the effect may actually be due to multiple treatments. However, if the study involved random assignment to ensure no differences between treatment groups and controlled for lurking variables, these threats can be minimized. In this context, none of the options A), B), or C) would be a threat to the internal validity, assuming that the study has been well-designed with proper randomization and control measures in place.