You might feel tired after solving a difficult math problem or studying for a whole day.Are our brains （大腦） really "burning （燃燒）" when we spend a lot of time thinking？In fact，our brains never stop burning calories （卡路里），even if we aren't thinking about anything.
   Our brain gets energy （能量） from a kind of sugar that is in rice and noodles.Our brain never really rests，it is burning energy in the form of sugar all the time.Even when we sleep，our brain needs energy to keep our body working.These include breathing，digesting （消化），and keeping the body warm.
   The brain uses up 20 to 25 percent of the body's total （全部的） energy.That's 350 calories per day for a woman and 450 for a man.When you are five or six years old，your brain uses up to 60 percent of the body's energy，according to Live Science.
   When we are thinking hard，the brain burns more calories.In one study，researchers found that people who worked on a hard task on a computer ate around 200 more calories than those who were resting.That explains why you feel hungry and eat more after taking exams or studying for a long time.

（1）Where do our rains get energy from according to the passage？

A

A

A．From rice and noodles.
B．From breathing or sleeping.
C．From thinking or studying.
D．From resting or digesting.
（2）What does the underlined word "burning" mean？

A

A

A．Using up.
B．Getting less.
C．Improving.
D．Agreeing.
（3）How many calories does a man's body need a day？

D

D

A．Around 20 to 25.
B．Around 350 to 450.
C．Around 580 to 750.
D．Around 1，800 to 2，250.
（4）What did researchers find in the study？

D

D

A．People who were resting got hungry more easily.
B．People burned fewer calories if they were thinking.
C．People working on computers ate more than others.
D．People working on hard tasks burned more calories.
（5）What does the text mainly explain？

C

C

A．When our brains work.
B．Why people feel thirsty.
C．How brains burn calories.
D．Why some people eat more.