Many nations have pledged to reduce greenhouse gas emissions, but are falling short of the target reduction of 25 to 40 percent of 1990 levels.

VOA: standard.2009.09.28

And, furthermore, they are characteristic of the target gas element.

更进一步的说，它们是目标气体元素的特征。

麻省理工公开课 - 固态化学导论课程节选