Problem: I read this background article the other day: Many different chemical substances cause cancer. Dozens of chemicals in tobacco smoke, including nicotine, have been shown to cause cancer ( Figure below ). In fact, tobacco smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco can also cause cancer. Other chemicals that cause cancer include asbestos, formaldehyde, benzene, cadmium, and nickel. I am facing a new situation today: Two friends met after 20 years. Tom had been smoking tobacco all these years and had some health problems related to that, while Randy quit smoking 25 years ago. Using the knowledge I acquired from the background article, how should I answer correctly the following question regarding my new situation: Which friend had an increased risk of developing cancer of the lung?

A: Tom

Problem: I read this background article the other day: A baby is born with zones of cartilage in its bones that allow growth of the bones. These areas, called growth plates , allow the bones to grow longer as the child grows. By the time the child reaches an age of about 18 to 25 years, all of the cartilage in the growth plate has been replaced by bone. This stops the bone from growing any longer. Even though bones stop growing in length in early adulthood, they can continue to increase in thickness throughout life. This thickening occurs in response to strain from increased muscle activity and from weight-lifting exercises. I am facing a new situation today: John was a relatively thin and bone-y child when he was younger. He would often get bruises and was prone to breaking bones. As an adult however he does lots of weight lifting and hasn't broken a bone yet. Using the knowledge I acquired from the background article, how should I answer correctly the following question regarding my new situation: Will lifting weights likely increase or decrease bone thickness?

A: increase

Problem: I read this background article the other day: Scientists think that the earliest flowers attracted insects and other animals, which spread pollen from flower to flower. This greatly increased the efficiency of fertilization over wind-spread pollen, which might or might not actually land on another flower. To take better advantage of this "animal labor," plants evolved traits such as brightly colored petals to attract pollinators. In exchange for pollination, flowers gave the pollinators nectar. I am facing a new situation today: Scientists studied two groups of plants. Group F had plants with flowers, group W had plants that fertilize over wind- spread pollen. Flowering plants were more efficient. Using the knowledge I acquired from the background article, how should I answer correctly the following question regarding my new situation: Which group of plants has a lower fertilization efficiency?

A: group W

Problem: I read this background article the other day: Recall that air pollution is due to chemical substances and particles released into the air mainly by human actions. When most people think of air pollution, they think of the pollution outdoors. But it is just as easy to have indoor air pollution. Your home or school classroom probably doesn't get much fresh air. Sealing up your home reduces heating and cooling costs. But this also causes air pollution to stay trapped indoors. And people today usually spend a majority of their time indoors. So exposure to indoor air pollution can become a significant health risk. I am facing a new situation today: Two twin sisters, Bianca and Rosa, were exposed to high levels of air pollution. While Bianca was exposed mostly to indoor pollution, Rosa was heavily exposed to outdoor pollution. Using the knowledge I acquired from the background article, how should I answer correctly the following question regarding my new situation: Which sister got more fresh air?

A:
Rosa