Suppose the decision variables in this problem are defined as Xij where i represents the starting node and j represents the ending node of an arc in the above network.

Which of the following statements are true?

XCD will be a decision variable in the linear programming formulation.

XAC $+$ XBC $$ XCD $$ XCE

$<=$

$30$ is a constraint in the formulation.

XBD $+$ XCD $+$ XDE $+$ XDF $=15$ is a constraint in the formulation.

XAB $+$ XAC

$>=$

$100$ is a constraint in the formulation.

XEF $$ XCE $$ XDE

$>=$

$15$ is a constraint in the formulation.

Exactly two answers are correct.