E

American doctors say mothers who smoke cigarettes may slow the growth of their children’ s lungs (肺). They said reduced lung growth could cause the children to suffer breathing problems and lung diseases (疾病) later in life. Doctors studied more than 1 100 children between the ages of five and nine. The mothers of some of the children smoked; the other mothers did not. Doctors tested the children once a year for five years to see how fast their lungs were growing. The test measured the amount of air the children could blow out of their lungs in one second. Children should be able to blow out more air each year because their lung-power increases as their lungs develop. But the doctors found that the lungs of the children whose mothers smoked had not developed as fast as they should. Doctors are not sure when the mothers’ smoking affected (影响) the children’s lungs. They say it could have happened before birth because the mothers smoked during pregnancy (怀孕) or it could have happened later when the children breathed smoke-filled air at home. Doctors also are not sure if reduced lung growth will affect the children’ s health when they have grown up. But they do know that children whose mothers smoked developed 20% more colds, flu (流感) and other breathing diseases than other children. So doctors feel there is a greater danger that such children will develop serious lung and breathing diseases later in life. Another recent study found that smokers have a greater chance of developing lung cancer (癌症，肿瘤) if their mothers smoked. That study found that the danger of lung cancer increased only for sons and .not for daughters. And it found that father’s smoking did not affect a person’s chances of developing lung cancer.

A best title for this passage might be______.