Which of these methods is not safe for thawing foods? A. In the refrigerator B. Under cold running water C. Under hot running water D. In the microwave?

Depending on what you are thawing, both a microwave and hot water wouldn't be recommended, like meat, if you ran raw meat under hot water or immediately in the microwave it is going to cook a bit but it will still be raw.

Refrigerating is a safe way to thaw but it would take a day or a few to thaw your food, as well as cold water, cold water defrosts at a cool temperature not heating the foot / meat or whatever immediately.

In this case I would say that the unsafe method would be running under hot water.