thousands of workers built the Great Wall of China被动语态

问题描述:

thousands of workers built the Great Wall of China被动语态
thousands of workers built the Great Wall of China
变被动语态是,the great wall was built by thousands of workers.
为什么built没有变成过去分词?
很着急,

建造的原型是build
过去式和过去分词都是built