In recent years, teachers of introductory courses in

Asian American studies have been facing a dilemma

nonexistent a few decades ago, when hardly any texts

in that field were available这是全文首句。迷惑的是when这个状语从句是修饰以下哪个成分

1，全句，即when是修饰teacher....facing a dilemma,

2,先行词a few decades ago.

那就是说when是定从，非限定修饰先行词 a few decades ago了？但是when不是只能做状语的吗？

还有怎么判断什么时候when修饰全句，什么时候修饰先行词？

好像又是语法了，呵呵