The correct answer is (a) Concave Lens.
A concave lens is a lens that curves inward at the center, like the inside of a bowl. It is used to correct myopia, or nearsightedness, which is a condition in which people can see objects that are close to them clearly, but objects that are far away appear blurry.
A convex lens is a lens that curves outward at the center, like the outside of a ball. It is used to correct hyperopia, or farsightedness, which is a condition in which people can see objects that are far away clearly, but objects that are close to them appear blurry.
A cylindrical lens is a lens that is curved in one direction but flat in the other. It is used to correct astigmatism, which is a condition in which the cornea, or the clear front part of the eye, is not perfectly round. This can cause vision to be blurry at all distances.
None of the above is not a correct answer.