動詞 fall behind:

1. retreat
   同義詞：fall back, lose, drop off, recede
2. hang (back) or fall (behind) in movement, progress, development, etc.
   同義詞：lag, dawdle, fall back

1. The major world powers are afraid of falling behind in the arms race.
   世界各大強國均惟恐在軍備競賽中落後。
2. France has fallen behind (Germany) in coal production.
   法國在產煤方面落後(於德國)了。
3. I've fallen behind with my correspondence.
   我積壓了許多信沒回。
4. Don't fall behind with the rent, or you'll be evicted.
   不要逾期不繳房租，否則會被逐出。