The enriching process for refined grains adds back: a:folic acid b: thiamin & niacin c:iron d: all of the above

The answer is D: all of the above. The enriching process for refined grains involves adding back certain essential nutrients that are lost during the refining process. These nutrients include folic acid (a type of B-vitamin), thiamin (also known as vitamin B1), niacin (another B-vitamin), as well as iron.

If you want to find this information yourself, a good place to start is by looking up the enriching process for refined grains. You can use search engines like Google and enter keywords such as "enriching process for refined grains" or "nutrients added back to refined grains during processing." This will give you various sources, including articles, research papers, and official websites, where you can find reliable information about the topic.

When reading these sources, you should look for information on what nutrients are added back during the enriching process. In this case, you will come across the fact that folic acid, thiamin, niacin, and iron are the nutrients typically added back to refined grains. By evaluating multiple sources and cross-referencing the information, you can ensure that you have an accurate answer to your question.