2. Foster discusses some theories behind why sleep is so important. In his third theory, what examples does he give of how sleep helps us cognitively?

exposure to hazardous carcinogens and toxic substances can cause breathing problems, such as copd and various types of cancer. it also increases the risk of heart attacks and strokes and has serious (but no less unattractive) side effects, such as aging, yellow teeth, a terrible smell and damage to the vocal cords.