人口自然增长率最低的大洲（   ）

   More and more people like bicycling and it is no surprise. It is fun, healthy and good for the environment. Maybe that's why there are 1.4 billion bicycles and only 400 million cars on roads worldwide today. Bikes can take you almost anywhere, and there is no oil cost!
   Get on a bicycle and ride around your neighbourhood. You may discover something new all around you. Stopping and getting off a bike is easier than stopping and getting out  of your car. You can bike to work and benefit (受益) from the enjoyable exercise without polluting the environment. You don't even have to ride all the way.
   Folding (折叠) bikes work well for people who ride the train. Just fold the bike and take it with you. You can do the same on an airplane. A folding bike can be packed in a suitcase. You can also take a common bike with you when you fly. But be sure to look for information by getting on airline websites. Not all airlines are bicycle-friendly to travellers.
   Health Benefits of Bicycling:
   It helps to prevent heart diseases.   
   Bicycling helps to control your weight.
   A 15-minute bike ride to and from work three times a week burns off five kilos of fat in a year.
   Bicycling can improve your mood (心情).
   Exercise  like  bicycling  has  been  shown  to  make  people  feel  better,  more  relaxed  and self-confident.
   Bicycling is healthier than driving.