Smoking bans in public places are linked with falls in childhood asthma   attacks and preterm births  , according to the biggest analysis of the influence of public smoking bans on child health. The finding should remove fears that such laws could have the opposite effect because they may lead people to smoke more at home. Several countries, such as Japan and Australia, have tightened laws on smoking in public places over the last few years. Meanwhile, some countries, such as the Netherlands and Germany, still allow smoking in pubs and restaurants. Only about half of US states have comprehensive bans, and there are few restrictions in poorer nations. Opponents often claim that bans could result in people smoking more at home, which would be worse for their children's health. Asthma is one of the main concerns as second-hand smoke harms children's airways in several ways. Researchers led by Jasper Been at Maastricht University Medical Centre reviewed as many as 11 studies that examined how hospital admissions for childhood asthma and preterm births changed after smoking bans came in. The studies involved more than 2.5 million births, and nearly 250,000 hospital admissions for asthma. The result shows that both asthma admissions and preterm birth rates fell by about 10 percent within a year after smoking restrictions were carried out. The effect on preterm births could also have been caused by pregnant women being more likely to quit or cut down following a public ban, says Been. But Been also says the studies could not completely prove that smoking bans directly caused these changes. However, as a matter of fact, because the analysis included several smoking bans introduced in different countries in different years, and most saw health improvements. Such findings are useful for countries and states where there is ongoing debate about how strict smoking bans should be, especially as hospital care for premature babies is so expensive. This might be one of the most important things to know in order to strengthen legislation  . Other studies have shown that rates of heart attack and stroke also tend to fall after smoking bans are introduced. In their analysis, the researchers drew their conclusion by
comparison experimenting questionnaire example
Question: Smoking bans in public places are linked with falls in childhood asthma   attacks and preterm births  , according to the biggest analysis of the influence of public smoking bans on child health. The finding should remove fears that such laws could have the opposite effect because they may lead people to smoke more at home. Several countries, such as Japan and Australia, have tightened laws on smoking in public places over the last few years. Meanwhile, some countries, such as the Netherlands and Germany, still allow smoking in pubs and restaurants. Only about half of US states have comprehensive bans, and there are few restrictions in poorer nations. Opponents often claim that bans could result in people smoking more at home, which would be worse for their children's health. Asthma is one of the main concerns as second-hand smoke harms children's airways in several ways. Researchers led by Jasper Been at Maastricht University Medical Centre reviewed as many as 11 studies that examined how hospital admissions for childhood asthma and preterm births changed after smoking bans came in. The studies involved more than 2.5 million births, and nearly 250,000 hospital admissions for asthma. The result shows that both asthma admissions and preterm birth rates fell by about 10 percent within a year after smoking restrictions were carried out. The effect on preterm births could also have been caused by pregnant women being more likely to quit or cut down following a public ban, says Been. But Been also says the studies could not completely prove that smoking bans directly caused these changes. However, as a matter of fact, because the analysis included several smoking bans introduced in different countries in different years, and most saw health improvements. Such findings are useful for countries and states where there is ongoing debate about how strict smoking bans should be, especially as hospital care for premature babies is so expensive. This might be one of the most important things to know in order to strengthen legislation  . Other studies have shown that rates of heart attack and stroke also tend to fall after smoking bans are introduced. In their analysis, the researchers drew their conclusion by
A. comparison
B. experimenting
C. questionnaire
D. example
Answer: