Which of the following is a correct definition of in extremis？

A、Whencollisioncannotbeavoidedbyactionofthegivingwayvesselalone
B、Whenthecompassbearingofonevesselfromtheotherdoesnotappreciablychange
C、Whencollisionhasbecomeunavoidablebyanactionofthevesselsinvolved
D、Thereisnoprecisedefinition