What does the word “snowball” in Paragraph three most probably mean.第一次Why do smokers tend to weigh less than nonsmokers and gain weight when they give up the habit?Contrary to “common knowledge”, nonsmokers do not generally eat more than smokers, nor do they exercise less, studies find. Research performed on smokers at rest indicates that nicotine (尼古丁) itself can increase basal metabolic (新陈代谢的) rates, meaning smokers burn more energy than nonsmokers during periods of inactivity. But surveys suggest most smokers smoke not while completely at rest, but while performing light activities such as desk work that can increase metabolic rates by two or three times. Unless nicotine’s metabolic effects increase proportionally with metabolic rates, its influence on weight might be insignificant.Now a study shows that nicotine’s effects on body-fuel consumption indeed increase proportionally with increases in activity. “These results indicate that the metabolic effect of nicotine may play a greater part in accounting for body-weight differences between smokers and nonsmokers than was previously believed,” says Kenneth A. Perkins and his colleagues at the University of Pittsburgh School of Medicine.