$11.$ The operating characteristic $($OC$)$ curve shows the probability of

a$.$ rejection for every possible true percentage of defectives

b$.$ acceptance for every possible true percentage of defectives

c$.$ making type I errors for various percentages of defectives

d$.$ none of the above

$12.$ If an artificial variable remains in the solution with a positive value after the stopping criterion has

been reached, the problem

a$.$ is infeasible

b$.$ is optimal

c$.$ needs a new basis

d$.$ has more than one solution