Answer:A) cotton
A fiber if available in trace or appropriate amount can link a suspect to a crime.Solubility is a preliminary test performed for identification of the type of fiber. In this method small amount of fiber evidence is dissolved in the suitable solvent to identify it's type. Some fibers completely get solublize in the solvent, some get partially soluble and other can only change their color or do not dissolve at all.
According to the given situation, the fiber dissolved in hydrochloric acid can be cotton. As the fibers of cotton are soft and slender and will get easily solubilize in hydrochloric acid.