principal signal

例句：

1. 1. The new policy isa major signal of the government'sintention to improve education quality.
   新政策是政府提高教育质量意图的主要信号。
2. 2. Thediscovery of this new species is a significantprincipal signal for understanding the evolution of lifeon Earth.
   这一新物种的发现是理解地球上生命演化的重要主要信号。
3. 3. Thecompany's announcement was a clear principalsignal that it would not be investing inthe project.
   公司的公告是一个明确的信号，表明公司不会投资该项目。