我来说吧,这个句子的正常顺序应该是It is feared that air quality in many of the world's major cities will deteriorate beyong reason unless pollution reduction measures are able to keep pace with the continued pressures of urban growth.
倒装了一下,真正的主语就是air quality。 it is feared只是引导作用,后面那个应该叫什么?条件状语从句?
不好意思,我不大习惯分析句子结构……反正顺序应该是我上面说的那样。