为什么I=S？

不想回答你这数学有问题的题目。回去好好再看自己遗漏了什么东西，太严重了

I = S applie to a closed economy only; there is no international trade at all. The national saving (S) will be used to support investment (I) spending. It is an identity equation in National Accounting (western standard)

储蓄消费发生在家户部门，生产投资发生在企业，企业的剩余看作存货投资

When has open economy and gov,
Public saving=BB(budget balance)
NX=X-IM
BB=G-T
S=Y-C-T
Y=C+I+G+X-IM
I=S+BB-NX

Public saving=BB(budget balance)
S is individual savings.

kankan