According to paragraphs 3 and 4, complex organic compounds probably have first appeared on Earth by the way that A. they might have been transformed from comets and asteroids. B. they might have arrived to Earth as our solar system passed through an interstellar nebula. C. they might have created when the newly appeared Sun led solid materials of the solar nebula to decompose. D. they might have come from reactions inside the solid materials that made up the early Earth.