Answer:
c. only the independent variable could have caused the results
Explanation:
Internal validity is a term in research methodology which explains the extent to which a study reach conclusion in a trustworthy cause-and-effect relationship that exists between a treatment and an outcome, such that, only the independent variable could have caused the results
Hence, in a given study, to have an internal validity, the researchust establishes a conclusion in which there is no alternative explanations for a finding the effect aside the independent variable.
