The correct answer is: Both a and b.
Classical physics is a term used to describe the collection of theories that existed before the advent of modern physics. It includes the study of mechanics, electricity and magnetism, optics, thermodynamics, and acoustics.
Optics is the study of light and its properties. It includes the study of how light is reflected, refracted, and diffracted.
Thermodynamics is the study of heat and its relationship to other forms of energy. It includes the study of temperature, pressure, and entropy.
Both optics and thermodynamics are part of classical physics.