Question

review the third and fourth paragraphs.
3 so what causes this vision problem? consider how the eye works. when you look at an object, the light rays of that object pass through the outermost layer of the eye (the cornea) and the lens. the cornea and the lens refract, or bend, the light and focus it on the light - sensitive tissue at the back of the eye (the retina). if you have perfect vision, the rays focus directly on the surface of the retina. in a myopic eye, the eyeball is usually too long from front to back. this causes light rays to focus at a point in front of the retina, rather than directly on its surface. this makes distant objects appear blurry.
4 myopia can also be the result of a cornea that is too curved or a lens that is too thick. for some, myopia is caused by a combination of these problems.
how do the third and fourth paragraphs work together?
they present a primary cause and then other potential causes.
they offer a scientific explanation and then a non - scientific one.
they explain how something works and then how it can be improved.

Explanation:

Paragraph 3 presents the primary cause of myopia (eyeball being too long). Paragraph 4 presents other potential causes (cornea too curved or lens too thick).

Answer:

They present a primary cause and then other potential causes.