分析英语结构

问题描述:

分析英语结构
an american engineer made important developments in bar codes in the 1960s,since when bar codes have been widely used.
since when句在句中充当什么成分?

since 表示时间的限定,自从什么什么以来,接bar codes have been widely used
when也是一个时间状语,因为bar codes have been widely used(in that age)表示在那个年代(in which=where)