The graph below shows the lung function of test subjects at three different ages who had exposure to ozone gas from the same source and location. According to the graph, which statement best describes the effects of ozone on human health?

At 0.2 ppm, lung function is worse in subjects older than 20.
At 0.3 ppm, lung function is better in subjects older than 20.
Subjects at age 20 have higher lung function than subjects at age 33.
Subjects at age 27 have lower lung function than subjects at age 20.