求翻譯 One theory is that with decreased exposure to sunlight,the biological clock that regulates mood,sleep,and hormones is delayed,running more slowly in winter.Exposure to light may reset the biological clock.Another theory is that brain chemicals that transmit information between nerves,called neurotransmitters (for example,serotonin),may be altered in individuals with SAD.It is believed that exposure to light can correct these imbalances.Chen says people who suffer from "the autumn blues" often are extremely fatigued,lack energy,need more sleep,crave carbohydrates,feel increased appetite and gain weight."It is a sad season,but you can try to make it happy.Remember,spring always lives in your heart," Chen says.