阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。
A migraine(偏头痛)can cause disabling pain. People may not feel back to normal for hours or even days. Migraines are most common among young adults and middle-aged people. In the United States, about eighteen percent of women and six percent of men report having migraines.
People who suffer from migraines can find that different “triggers”(诱因)in different people may get a headache started. Stress can act as a trigger. So can chocolate in some people. Many migraine sufferers say hot weather and low barometric pressure(大气压)can act as triggers. But researchers say they haven’t got much scientific evidence of that until now.
In a new study, a team examined the medical records of seven thousand hospital patients. The patients had visited the emergency room at Beth Israel Deaconess Medical Center in Boston, Massachusetts, because of a headache. More than two thousand of them had been found to have a migraine.
The team then compared those records to weather conditions in the twenty-four hours before the hospital visits. For every increase of five degrees centigrade in air temperature, the patients had a seven and one-half percent higher risk of migraines. Decreases in barometric pressure two to three days before the visit also appeared to trigger headaches.
The researchers found no evidence that air pollution influenced headaches. But they could not rule out the possibility of a smaller effect.
A separate study has found that age, gender, and where a person has extra body fat may affect the risk of migraines. It found that overweight people between the ages of twenty and fifty-five may have a higher risk. On average, those who were larger around the middle were more likely to have migraines than those of the same age with smaller waistlines.
The study involved twenty-two thousand people. It was led by Lee Peterlin. She says early results suggest that losing weight in the stomach area may help younger people who experience migraines, especially women.
