Which aspect determines a health source's credibility?

the age of the author

the type of medium (online versus print)

the author's credentials

the country of publication

The correct answer is C.

An author's credentials can determine a health source's credibility. None of the other options would apply to credibility. When it comes to health, if you want to make sure that what you are researching or reading is authentic and reliable you need to find out whether the author is a professional health expert or not. You can do this by finding out their credentials.