At The Rockefeller University in New York, she is currently studying how skin forms from precursor stem cells, looking for clues that could help researchers understand how defective stem cells can cause cancers and other disorders.

VOA: standard.2010.03.29

So, she had a precursor. So what? Does that make any difference?

所以，在她之前有过别人，那有怎样，会造成不同吗？

耶鲁公开课 - 1945年后的美国小说课程节选

And so, you make not only water vapor, NOX but you make some nitrous oxides, NOX, or nox as it is known, and this is the precursor to smog.

这样不仅仅得到的水蒸气，但是你会得到一些氮氧化物，或者如大家所知到的nox，这是烟雾的前驱体。

麻省理工公开课 - 固态化学导论课程节选