Concept: Shadows and eclipses are formed because light travels in straight lines.Explanation:When an opaque object blocks light, the light cannot bend around it; it travels in a straight line.This creates a dark region behind the object called a shadow.An eclipse is a large-scale shadow cast when one celestial body blocks light from another.This behaviour is known as the rectilinear propagation of light.Answer: B. Rectilinear propagation of light