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?
答
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)