根据短文内容及首字母提示在空白处填上适当的单词，使短文意思完整。

        Airplanes are the newest kind of transportation. From early times, people tried to f     1    through the

sky like birds. About 100 years a     2     , someone took the first ride on an airplane. This ride lasted for less

than one m     3   . These first planes were very s     4    , too. Only one o     5    two people could fly in

them at one time.

        Today these p     6    are very big and fast. H     7    of people can travel in them at one time. W     8    

them, people can get f     9    one side of the United States to the other in less than one day. Traveling is very

d   10   from the way it was 100 years ago.

1._____ 2._____ 3._____ 4._____  5._____

6._____ 7._____ 8._____ 9._____ 10._____

简述同步电机的“同步”是什么意思？