Answer: option d. all of the above.
Explanation:
A mineral is an element or a inorganic compound that existes in nature as solid cristals; usually combined with other minerals in ores.
Some examples of minerals, among many, are titania, wich is TiO2, zirconia, which is ZrO2, silica, which is SiO2, gold, Au, silver, Ag.
As you see the definition and examples given meet the whole features included in the stament: a. the have a chemical formula, b they occur naturally, and c.have a characteristic internal structure (that is the way how the atoms are arranged in the specifi cristal).
