forerunner|forerunners

持续的咳嗽可能是流感的先兆。

Persistent cough can be a ___forerunner of the flu.

这些早期的抗议活动是后来大规模革命的前兆。

These early protests were the ___forerunners of the massive revolution that followed.

蒸汽机是现代工业发展的先驱。

The steam engine was the ___forerunner of modern industrial development.