Aglobal alignment algorithm (such as the needleman-wunsch algorithm) is guaranteed to find an optimal alignment. such an algorithm:
a) puts the two proteins being compared into a matrix and finds the optimal score by exhaustively searching every possible combination of alignments.
b) puts the two proteins being compared into a matrix and finds the optimal score by iterative recursions.
c) puts the two proteins being compared into a matrix and finds the optimal alignment by finding optimal sub-paths that define the best alignment(s).
d) can be used for proteins but not for dna sequences %.