If you have farsighted eyes, you need lenses that light. A. focus B. reflect C. absorb D. spread out

Option A Focus  

Explanation:

The reason is that the farsighted eyes have issues with the rays that focuses at wrong place which means that the light rays must be focused on a particular point for which convex lenses are used. The convex lenses focuses the rays on point where the picture becomes clear and this is reason why convex lenses are used.

an obstruction

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.