回上一层第四部 第十课 --- 请重复跟读，直到可以於声音档的留空之间唸完整句為止；熟练之后您必将可以 "脱口而出" 地说出标準的美式英语
- every so often
- Every so often I like to go sailing with my friends.
- fall behind
- Dorothy fell behind in class, but she didn't give up.
- During the tour, I fell behind and couldn't catch up.
- fall flat
- Your best design fell flat in the contest.
- fall off
- The economy has been falling off for last five years.
- The revenue from the football stadium has fallen off over the years.
