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Which type of lenses represent a biconvex lens?

  1. cylinder lenses

  2. plus lenses

  3. minus lenses

  4. two plus surfaces

The correct answer is: two plus surfaces

A biconvex lens is a type of lens that is curved outwards on both sides. In comparison, a cylinder lens only has one curved surface, while minus lenses are curved inward and do not have the outward convex shape. Plus lenses generally have a convex shape, but they are not necessarily biconvex. The only option that includes two outwardly curved surfaces, making it biconvex, is D two plus surfaces. Therefore, D is the correct answer.