Answer the two following questions in two paragraphs:Why is internal validity of a study

Answer the two following questions in two paragraphs:
Why is internal validity of a study important? Using the article you are critiquing, give an example of a potential threat to internal validity that the authors might have encountered when designing their study
Why is external validity of a study important? Using the article you are critiquing, give an example of a potential threat to external validity that the authors might have encountered when designing their study