单选题 ADHD Linked to Air Pollutants Children have an increased risk of attention problems，seen as early as grade school , if their moms inhaled（吸入）a certain type of air pollution when they were pregnant. That's the finding of a new study. Released when things aren't burned completely, this pollution is known as polycyclic aromatic hydrocarbons, or PAHs. The biggest sources of these PAHs: the burning of fossil fuels, wood and trash. Frederica Perera works at Columbia University's Mailman School of Public Health in New York City. She researches how exposure to things in the environment affects children's health. In a new study , she and her team studied the exposure to air pollution of 233 nonsmoking pregnant women in New York City. Because burning tobacco can spew（排放） PAHs into the air and lungs, Perera's team focused on nonsmokers. The researchers wanted to probe（探查） other sources of PAHs, ones that would have been hard for an individual to avoid. The team started by testing the blood of each woman during pregnancy. The reason: Any PAHs in a woman's blood would also be available to the baby in her womb. Nine years later, the researchers investigated signs of attention problems in these children, now age 9. They asked each child's mother a series of questions. These included whether her child had problems doing things that needed sustained（长期的） mental effort, such as homework or games with friends. The scientists also asked if the kids had trouble following instructions or made frequent, careless mistakes. All of these can be symptoms of a disorder called Attention Deficit Hyperactivity Disorder, or ADHD. About one in 10 U.S. children has ADHD. Among the women studied, traffic and home heating were the primary sources of air pollution exposure, Perera and her team suspect. Some of these women had low levels of PAHs in their blood. Others had high levels. Those with high levels were five times as likely to have children who showed attention problems by age 9. The new findings were published November 5 in the journal PLOS ONE.

单选题 Perera and her team chose nonsmoking pregnant women all over America.

单选题 The main purpose of the research was to find out how exposure to PAHs played a role in harming the subjects' physical health.

单选题 Nonsmoking mothers were selected because the effect of smoking on PAHs was unclear.

单选题 The blood of each women was tested once a month during pregnancy.

单选题 Kids with ADHD commonly fail in school.

单选题 The women with high levels of PAHs in their blood were more likely to have kids with ADHD.

单选题 Traffic and home heating were considered to be the biggest sources of PAHs for the subjects in the research.