다음 밑줄 친 부분 중 어법상 틀린 것은??

Raised in a poor family, Confucius truly understood the suffering of the people. In his view, the lords of his country, only interested in their own personal gain, ①were responsible for it. Therefore, he gathered a group of intelligent followers ②what he trained in several subjects including ethics. He believed that government leaders must be humane, honest and ③fair, not experts in administration. He taught his students that it is the role of rulers ④to secure the happiness of their people. He had considerable success in placing his pupils in positions of power in government. When the men who ⑤had been trained by him were sent into service, even immoral rulers valued their honesty.

정답과 자세한 설명 부탁드립니다^^