$[1]$ The following network diagram represents a minimum cost transshipment problem.

Assume that $x_{ij}$ is represents the quantity shipped from node $i$ to node $j.$

Which of the following statements are true?

$($a$)$ There will be exactly one constraint containing exactly $3$ decision variables.

$($b$)$ Both $x_{BC}$ and $x_{CB}$ will be decision variables in this problem.

$($c$)$ The objective function contains a term $"+5x_{CB}"$ among others.

$($d$)$ None of the above.