Read the paragraph. Read the question and choose the correct answer.
Sleep is a condition of your body and mind in which your nervous system is relatively inactive.
Your eyes are closed, your muscles are relaxed, and consciousness is mostly suspended for several hours. There are 24 hours in one day, 168 hours in a week, and 8,760 hours in a year. The average amount of sleep that many people get each day should be about 8 hours, which is one-third of a day.
If you live to be 90 years old, you will sleep for 30 years. Every living thing needs sleep and rest.
What is sleep, according to the text?

• It is a condition of your body and mind in which your consciousness is clouded.
• It is a condition of your body and mind in which your muscles are tense.
• It is a condition of your body and mind in which your nervous system isn't active.
• It is a condition of your body and mind in which your eyes are tired.