Suppose that we are minimizing a linear function f(x)=c x, over a set X={x:Axb}. Assume that X is non-empty (i.e., the problem is assumed to be feasible). Let X denote the set of optimal solutions, so that X X. Which of the following could occur? Mark all that apply. X could be empty X could consist of a single point X could consist of infinitely many points forming a bounded polytope. X could be unbounded