Of all the changes that have taken place in English-language newspapers during the past quarter-century, perhaps the most far-reaching has been the inexorable decline in the scope and seriousness of their arts coverage.
that 修饰changes , that 做成分,主语 → 定语从句
the most far-reaching (changes)---change 作为主语省略,所有保留the most far-reaching
A of B 翻译:B的A