Regular Reflection
Regular reflection is the phenomenon where light waves strike a smooth surface and bounce back in a predictable, straight-line manner. This occurs when the surface is highly polished or smooth, allowing the light waves to reflect at the same angle as they strike the surface.

Explanation of Options
a) Marble flooring with oil spread over: In this case, regular reflection will still take place because the oil spread over the marble flooring does not affect the smoothness of the surface. The light waves will still reflect in a predictable manner.

b) Mirror: Mirrors are specifically designed to have a highly polished and smooth surface. This ensures that regular reflection occurs when light waves strike them. Therefore, regular reflection will take place when a beam of light strikes a mirror.

c) Shiny metal sheet: The correct answer is option 'C'. Regular reflection will not take place when a beam of light strikes a shiny metal sheet. Shiny metal surfaces have a highly polished and smooth surface, similar to mirrors. However, unlike mirrors, metals also have the ability to absorb and scatter light. This leads to irregular reflection, where the light waves bounce off in different directions rather than following the law of reflection.

d) Unpolished wooden surface: In the case of an unpolished wooden surface, regular reflection will not take place. Wood is not a smooth surface, and its texture and roughness cause the light waves to scatter in various directions upon striking it.

Conclusion
Regular reflection occurs when light waves strike a smooth surface such as a mirror or a polished surface. Shiny metal sheets do have a smooth surface, but the ability of metals to absorb and scatter light leads to irregular reflection. Unpolished surfaces like wood do not have a smooth surface, causing the light waves to scatter in different directions.