In the following statements about nonlinear programming (NLP), which one is correct?

a) Multiple local optimal solutions always exist in an NLP problem.

b) If the unconstrained NLP has a unique solution, then adding constraints to the NLP will not create additional local optimal solutions.

c) No matter it is maximization or minimization problem, the Lagrangian multipliers of an NLP must always be nonneagive at the local optimal point.

d) If a Lagrangian multiplier equals zero, it means the corresponding constraint is active.

e) None of the above.