Out of the options that are provided, aluminum foil would be the best reflector of light.  

To “reflect” means “to bounce off of.” Reflection of light occurs the best off of hard, smooth, and shiny surfaces. When bouncing off of such surfaces, light rays reflect at the same angle in which they hit the hard and shiny surfaces.

On the other hand, shiny and rough surfaces cause light to reflect in all directions. In other words, shiny and rough surfaces cause light to scatter.

The reflection of light is minimal when light hits a soft, opaque, and rough surface. The shower curtain would be an example of such a material.

Light would not reflect much off of the drinking glass or sealable plastic bag. Instead, light would mostly pass through such transparent materials.