What is the best possible way to verify claims a manufacturer makes about a supplement's safety and effectiveness?
the manufacturer's website
the product's commercial advertisement
the us food and drug administration website
a consumer's blog review

The most appropriate way to verify the claims made by the manufacturers regarding the safety and effectiveness of a specific supplement would be to go to the website of the manufacturer and see the reviews, look for the studies behind their product, and questioning around.  

As supplements are generally monitored by the Food and Drug Association, the manufacturers are generally provided with the honor system to provide precise knowledge to the consumers. Thus, performing self-research will assist enormously.  

answer: d is correct