Sue has been attending university for about a month. During the past week, she has been having trouble sleeping, experiencing headaches, and is having trouble concentrating, especially when she has an upcoming test. A lack of sleep can be both a cause and an effect of stress. In order to overcome insomnia Sue should consider A) using her bed only for sleeping, not for studying. B) taking a nap when she feels tired. C) exercising just before going to bed to release excess stress. D) sleeping in on weekends.