The correct answer is A. Rectilinear propagation of light.
Light travels in straight lines. When an object blocks light, a shadow is formed on the opposite side of the object. The shape of the shadow depends on the shape of the object.
Reflection is the bouncing of light off a surface. Refraction is the bending of light as it passes from one medium to another. Total internal reflection is the phenomenon that occurs when light passes from a medium with a higher refractive index to a medium with a lower refractive index at an angle greater than the critical angle.
In the case of shadows, reflection and refraction do not play a role. The shadow is formed because light travels in straight lines and is blocked by the object.