In the minimum spanning tree problem formulation, the subtour elimination constraint can be formulated as: a. E' = "=1*ij = |SI - 1, Vi, je 1..n), and i # j 1 where |S: the cardinality of subset S, and for all S CV b. none of the mentioned c. - '(x1+x):) = 1 d. xij + xji 2 1. Vi, j (1...n) e. Xij + xj. S 1, Vi, je (1...)