$15-$ Which of the following national income accounting identities is INCORRECT?

a$)$ Sh $+$ Spu $$ I $=$ X $$ M

b$)$ Sh $+($M $$ X$)$ I $=$ DEF

c$)$ Sh $+($G$$T$)=$I$+($X$$M$)$

d$)$ All of the previous identities are correct.