OA: A web site could be useful for a quick answer but not a very accurate one. Especially since these people arent certified in food.
OB: A book sounds like a very credible place to look for answers but this book is more about personal experiences in diets and isn't certified in food.
OC: An article sounds like a very credible source but is from a person who studied food related problems, meaning that what they have studied isnt as official as an actual certified worker in food.
OD: The most credible source for Ray to choose would be a book on gluten-free diets by an author who has two degrees in nutrition and works at the University of Rockingham.
