[经] marginal utility theory of interest

lì xī de biān jì xiào yòng lǐ lùn ㄌㄧˋ ㄒㄧ ㄉㄜ˙ ㄅㄧㄢ ㄐㄧˋ ㄒㄧㄠˋ ㄩㄥˋ ㄌㄧˇ ㄌㄨㄣˋ