This question is likely referring to the phenomenon of dispersion of light, where white sunlight is separated into its constituent colors. A shower of raindrops acts like a large number of tiny prisms. As sunlight enters a raindrop, it is refracted, dispersed into its spectral colors, reflected internally, and then refracted again upon exiting the raindrop. This process creates a rainbow, which is a visible spectrum of sunlight. A plane mirror reflects light but does not disperse it. A convex lens converges light, and while it can refract light, its primary function is focusing, not spreading or dispersing white light into a spectrum like a prism or raindrop does. A combination of lenses can be used for various optical purposes but typically not for simply spreading or dispersing sunlight into its spectrum in the manner suggested by the formation of a rainbow.