The amendment would prevent the U.S.Export-Import Bank from entering into any deals with foreign companies that significantly contribute to Iran's refined petroleum resources, part of efforts to pressure Iran to stop its uranium enrichment program.

VOA: standard.2009.06.23

It's a mechanism that they have evolved in order to prevent foreign genes from entering a cell and being expressed.

它们进化出这种机制来,防止异源基因进入细胞并表达

耶鲁公开课 - 生物医学工程探索课程节选

We're at a point now where some really important recent discoveries have not answered all our questions, but have certainly helped take us into some new directions and really open up a new chapter in the search for additional options to prevent HIV Those recent discoveries include anti-bodies found in some HIV positive people that prevent the AIDS virus from entering cells.

VOA: standard.2010.07.15