flit to and fro的用法和样例：
- Trucks shuttled to and fro on the high ways.
- He is walking to and fro in the room.
- The ship was rolling heavily to and fro.
- The signals go to and fro at a very high but almost constant speed.
- The cat made little rushes to and fro after the ball.
- The tall chimney tottered (to and fro) and then collapsed.