牛津译林 模块六第二单元 M6U2 Grammar and usage语法
2.有时为了强调，分词前可带when, while, once, if, though, although, as if, unless等连词一起作状语，以便句
子的 意思更清楚、更连贯。如： When comparing different cultures, we often pay attention only to the differences without noticing the many similarities. though tired, he still continued reading.