canary|canaries

这只金丝雀唱得很欢快。

This ___canary is singing happily.

这些志愿者被当作'金丝雀'（探路者）派往灾区评估情况。

The volunteers were sent as ___canaries to assess the situation in the disaster area.

那名新员工成了公司财务欺诈的预警信号，就像矿井中的金丝雀。

The new employee became the ___canary in the coal mine for the company's financial fraud.