After 10 weeks, neither group reported a case of the flu. which procedure would have made the outcome of this study more valid?

I think you forgot to give the options along with the question. I am answering the question based on my knowledge and research. "Test a third group that does not receive the supplement" would be the procedure that would have made the outcome of this study more valid. I hope the answer helps you.

Answercan utilize even low wind speed to produce electricity;