[经] law of diminishing marginal productivity

biān jì shēng chǎn dì jiǎn lù ㄅㄧㄢ ㄐㄧˋ ㄕㄥ ㄔㄢˇ ㄉㄧˋ ㄐㄧㄢˇ ㄌㄨˋ