One of the things she wrote about was life on a small farm a

One of the things she wrote about was life on a small farm at the beginning of the century是用was ,而不是were?在定语从句中,关系代词that,which等作主语时,其谓语动词的数不是与句中先行词一致吗?
One of the things she wrote about was life on a small farm at the beginning of the century是用was ,而不是were?在定语从句中,关系代词that,which等作主语时,其谓语动词的数不是与句中先行词一致吗?