A number of prominent economists have also argued that it's harder for the poor to climb the economic ladder today because the rungs (横档) in that ladder have grown farther apart.
2015年12月六级真题（第三套）阅读 Section C
柯林斯高阶英汉双解学习词典释义
Rung is the past participle of ring .
N-COUNT
梯级;横档
The rungs on a ladder are the wooden or metal bars that form the steps.