下表为世界人民反法西斯战争时间统计简表，从表中可看出：

   American boys and girls like watching TV. Some children spend six hours a day at school and four to six hours a day in front of the TV sets. Some children even watch TV for eight hours or more on Saturday.
   Television（电视）is like books and films . A child can learn good things and bad things from it. Some TV programs help children to understand the news, the people and places from other countries. With TV, children do not have to go out to see films, they can hear interesting music or watch a game at home. But some programs are bad for children, so parents sometimes help them to find other interesting and useful things to do.

若一个正多边形的每一个外角为30°，那么这个正多边形的边数是（　　）