A study has high internal validity if it:1 分has at least one confounding variable.produces results that are statistically significant.is conducted with a large number of participants.is free of confounding variables.

A study has high internal validity if it is free of confounding variables.

Here's why:

1. Having at least one confounding variable: This would actually decrease the internal validity of a study. Confounding variables are factors other than the independent variable that may cause or contribute to the effect. If these are not controlled, it's hard to know if the results are due to the independent variable or the confounding variable.

2. Producing results that are statistically significant: While this is important for showing that your results are not due to chance, it doesn't necessarily mean your study has high internal validity. You could have significant results, but if your study is full of confounding variables, the internal validity is still low.

3. Being conducted with a large number of participants: Having a large sample size can increase the external validity of a study, meaning the results are more likely to be generalizable to the larger population. However, it doesn't necessarily increase internal validity.

4. Being free of confounding variables: This is the correct answer. When a study is free of confounding variables, it means that the researchers have done a good job of ensuring that any changes in the dependent variable are likely due to the manipulation of the independent variable, not some other factor. This increases the internal validity of the study.