Read the short text. Read and complete the sentence with the correct part.

When a person sleeps, a person's brain maintains proper blood sugar levels, regulates hormones that control appetite and metabolism. A person's brain reduces high blood pressure. A good night sleep leads to better physical, mental and emotional health. A person may often feel cranky and tired, have a short temper. A person is unable to think clearly without enough sleep. A person may struggle with following instructions having an argument with parents or friends and has difficulty doing things that are usually easy to do. It becomes more difficult to concentrate and to remember things.

If people don't get enough sleep, ___

• they can concentrate badly.
• they cannot argue with parents or friends.
• they do different things very well.
• they can struggle with any difficulty.