The correct option is C Refraction
Answer is B.
A lens is a piece of glass (plastic) with two refracting surfaces, which are either curved (e.g., a segment of a sphere) or plain.
Lenses are used to form images by refraction in optical instruments (microscopes, telescopes, cameras, etc.)
There are two types of lenses: converging (thickest in the middle) and diverging (thickest at the edges).