Short-sight defect, also known as myopia, is a common eye problem where a person can see nearby objects clearly but cannot see distant objects properly. This happens when the eyeball is too long or the cornea is too curved. Because of this shape, light rays focus in front of the retina instead of directly on it.

To fix this problem, a concave lens is used. A concave lens is thin in the middle and thicker at the edges. It helps to spread out (diverge) the light rays before they enter the eye. This way, the light rays focus directly on the retina, and the person can see distant objects clearly again.

Let’s look at what the other options mean:
- **Convex lens** is used for long-sight or hyperopia, not short-sight.
- **Converging lens** is another name for a convex lens, so it also doesn’t help in this case.
- **None of these** is incorrect because a concave lens is definitely used for short-sight correction.

Many people use eyeglasses with concave lenses to correct myopia. These glasses help them see the board in a classroom, road signs while driving, or anything far away.

In summary:
- Short-sight = Myopia
- Corrected by = Concave lens (diverging lens)
- Result = Clearer distant vision

So, the correct answer is Concave lens, which helps bend the light correctly and lets the person see distant objects clearly.