●on a ˈknife-edge ( on a ˈrazor’s edge) in a very dangerous or difficult situation where there is a risk of sth terrible happening处于非常危险（或困难）的境地◆He was balanced on a knife-edge between life and death.他处于生死关头。◆The future of this company is on a razor’s edge.这家公司的未来凶多吉少。