Which of the following statements is true of "Earth’s Ozone Layer"?

JB: After 30 years of steady decline, Earth’s ozone layer is thinner but seems to be stable. A ban on ozone-depleting CFCs is largely responsible. Computer modeling gives reason to hope for an almost full recovery of Earth’s ozone layer within 60 years. But this sort of modeling is difficult -- and its predictions aren’t iron-clad.
DB: And some models show the ozone layer could face a new threat -- from global warming. Drew Shindell, an atmospheric scientist at NASA’s Goddard Institute for Space Studies in New York City, talked with us about his computer models of climate.

(With) Other viruses, such as smallpox and measles, and polioneuromere, the majority of people mount an immune response even if they never been vaccinated that clears the natural infection. With H1V, there are virtually no incidents of a person who has completely cleared the virus from their body, which means that although some people can control the virus better than others, the body is having trouble making a protective immune response.