They were revolted by conditions on the farm.

were 是 be 动词的过去式复数形式，表示"是"或"存在"的状态。 revolted 是动词 revolt 的过去分词形式，revolt 意思是"使厌恶、使反感"，这里与 were 构成被动语态，表示"被...所厌恶"。 by 是介词，在这里表示被动动作的执行者或原因，引出"厌恶"的来源。 were revolted by 这个被动结构整体表示"被...所厌恶/反感"，描述主语因某事物而产生强烈的厌恶情绪。