It is useful to be able to predict the extent to which a price change will affect supplyand demand.
问题描述：
It is useful to be able to predict the extent to which a price change will affect supply
and demand.
答
it:形式主语；is系动词,作谓语的一部分；useful表语,作谓语的一部分；to be able to predict the extent to which a price change will affect supply：真正的主语.真正的主语是一个不定式短语,其中the extent to wh...