② Iodine contained in laver can prevent goiter;

So the answer is: sugar; Iodine.

(2) Formaldehyde is toxic, which can destroy the structure of protein and make it lose its physiological function and inedible; Moldy peanuts contain Aspergillus flavus, which can induce diseases such as cancer; Steamed steamed bread with baking soda is harmless to human body.

So the answer is: B.

(3) Identification of synthetic fiber and wool by combustion method. Wool has the smell of burning feathers, and synthetic fibers are basically tasteless. Synthetic fibers generally shrink into pellets or melt when burning, so the simplest and most reliable method is C.

So the answer is: C.