In April,1994 unknown assassins shot down the plane carrying then-President Juvenal Habyarimana.

VOA: standard.2009.04.10

I could take an unknown gas and put it in and measure it and then say, wow, those are the lines that are characteristic of sodium.

我取一种未知气体，把它放到管里,然后检测它，哇，这些线是钠的特征。

麻省理工公开课 - 固态化学导论课程节选

I could take an unknown gas and put it in and measure it and then say, wow, those are the lines that are characteristic of sodium.

我取一种未知气体，把它放到管里,然后检测它，哇，这些线是钠的特征。

麻省理工公开课 - 固态化学导论课程节选