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 本意是"反抗、反叛"，引申为"使厌恶、使反感"。 by 在这里表示被动行为的施动者，引出导致厌恶情绪的原因。 were revolted by 构成被动语态结构，表示"被...所厌恶/反感"。