Questões de Concurso Militar Quadro Complementar 2017 para Segundo-Tenente - Ciências Náuticas - Área de Náutica

Which option is correct?

When a Search-and-Rescue Operation is in progress, the RCC or the OSC will instruct other vessels in the vicinity to keep radio-silence, unless they have messages about the accident. Radio silence is imposed to other vessels by the phrase