Do you know why you need to take exercise to keep fit？The following may help you know about it．

•It helps with addiction（癖嗜）control

The brain releases dopamine（多巴胺），which responds to any form of pleasure，be it sex，drugs，alcohol or food．Some people become addicted to dopamine and substances that produce it-especially drugs or alcohol．

Regular exercise can help in this addiction recovery as it effectively distracts you，making you de-prioritize your cravings．When faced with mental or emotional challenges in life，exercise can help you cope in a healthy way instead of resorting to alcohol，drugs or other negative behaviors that eventually only make your symptoms worse．Regular exercise can also help to strengthen your immune system．

※Your risk of diabetes（糖尿病）goes down

Within one week of your regular exercise，your sensitivity to insulin （胰岛素）becomes greater and that，in turn，lowers your blood sugar levels，reducing your risk of Type 2diabetes．

Also，exercise can decrease your stroke（中风） risk； given that two of the greatest risk factors for strokes are high blood pressure and heart disease，exercise with its benefits of a stronger heart and better circulation is important．

The U．S．Centers for Disease Control and Prevention recommends at least 30minutes of moderate exercise at least five days a week for good health，though you should always check with your doctor if you have any health concerns before beginning any exercise program．

※You're reducing stomach fat

When you do one month of regular exercise，your body ditches those extra fat and gains muscle．An Australian study shows that overweight people who took part in a four-week program of moderate exercise reduced stomach fat by 12percent．

21．Which is the best title of the passage？___

A．How to slim．

B．The ways of exercising．

C．The reasons for working out．

D．The effect of exercising on diabetes．