Tsis tshua muaj lub ntiaj teb, hu ua "cov khoom muaj nqis" ntawm cov ntaub ntawv tshiab, ua cov khoom siv tshwj xeeb, tuaj yeem txhim kho qhov zoo thiab kev ua tau zoo ntawm lwm cov khoom, thiab paub tias yog "cov vitamins" ntawm kev lag luam niaj hnub no. Lawv tsis tsuas yog siv dav hauv kev lag luam ib txwm muaj xws li metallurgy, petroc ...
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