At the same time, machine tool and die makets who provided all the precison parts and mechanical devices for the factory infrastructure flourished as techonology continued to improve,

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그리고 of which는 여기서 어떤 쓰임인건지요ㅜㅜ

the offshoots of which reared a range of new and exciting careers, particularly of interest to the large groups of young men returning from military duty around this time, and kept unemployment rates down while boosting overall spending.