A tax on upstream carbon sources is one easy way to put a price on carbon emissions, although some countries may wish to use other methods, such as emissions trading schemes.
出自-2017年6月閱讀原文
Now, instead of swimming upstream, we relax, sleep, watch movies, or listen to music.
2018年12月六級真題（第一套）閱讀 Section B
柯林斯高階英漢雙解學習詞典釋義
ADV
逆流地；往上游；在上游
Something that is moving upstream is moving towards the source of a river, from a point further down the river. Something that is upstream is towards the source of a river.