J$($X$)=-2$X$1$X$2+2$X$2+4$X$3-2$X$1$X$3$X$4+6$X$4+3$X$1-2$X$1$X$2$X$3$X$4.$ If we apply Sequential

forward Selection to completion, What will be the optimum feature subset?

a$.13$

$$ b$.12$

$$ c $10$

$$ d$\mathrm{.}11$