a dandruff shampoo claims it can eliminate all dandruff flakes for six months. Which would be a good strategy for providing the claim is true?

A.ask the one person you know used it to verify if it worked for her.
B. Ask the cashier if a lot of people have purchased this product.
C. Search online to see if the claims can be verified by scientific studies.
D.Buy it and just test it yourself over the next six months.
PLEASE HELP!!!!!!!!!!