Concept:Long sightedness is corrected by a converging lens that focuses light on the retina.
Explanation:In long sightedness, the eyeball is too short or the eye lens is too weak.
So, light rays from close objects form an image behind the retina, causing blurred vision.
A convex lens is thicker at the centre and makes light rays converge more strongly.
This brings the image forward to fall exactly on the retina.
As a result, the eye can see nearby objects clearly.
Concave and biconcave lenses spread rays apart, so they cannot correct this defect.
Hence, the correct optical device is a convex lens.
Answer:B. convex lens