spread是哪个单词的过去式

spread本身就是过去式。
例句：
The disease has spread at an alarming rate、
这种疾病已经以惊人的速度传播开来。
Using too much water could spread the stain、
用水太多可能使污迹扩散。

Prompt action was required as the fire spread、

由于火势蔓延，须要立即采取行动。

The clouds had spread and covered the entire sky、

乌云铺开，遮蔽了整个天空。

Fire spread rapidly after a chemical truck exploded、

一辆装有化学品的卡车爆炸后火势迅速蔓延开来。