Structure. Amethyst is a purple variety of quartz (SiO2) and owes its violet color to irradiation, iron impurities (in some cases in conjunction with transition element impurities), and the presence of trace elements, which result in complex crystal lattice substitutions.
The answer is C, work. The reaction of the air/gas mixture being ignited produces energy which moves the piston up and down which turns the crankshaft.
