打喷嚏可能是感冒的迹象。

Sneezing can be a ___sign of a cold.

天空中的乌云是下雨的征兆。

Dark clouds in the sky are a ___sign of rain.

他无法处理这种情况是弱点的明确迹象。

His inability to handle the situation is a sure ___sign of weakness.