Question $18(4$ points$)$

In a $$ integer model, the solution values of the decision variables are or $1.$

A$)$ total

B$)$ mixed

C$)0\mathrm{.}1$

D$)$ total, $0-1,$ and miked

Question $19(4$ points$)$

In a $0-1$ Integer programming model, if the constraint $x1-x2=0,$ it means when project $1$ is selected, project $2q,$ be selected.

can sometimes

must also

can also

can never