Which describes the affine gap measure?

a$.$ Computed by assigning a score to each alignment between the two input strings and choosing the score of the best

alignment

b$.$ An extension of the Needleman$-$Wunsch measure that handles longer gaps more gracefully

c$.$ Computes the minimal cost of transforming string x to string y

d $.$Designed to find matching substrings by introducing two key changes to the Needleman$-$Wunsch measure