When clustering only by dummy variables that represent categorical variables, the simplest measure of similarity between two observations is called the

a$.$ Jaccard's coefficient.

b$.$ antecedent.

c$.$ Euclidean distance.

d$.$ matching coefficient.

b$.$ considering only the two most dissimilar observations in the two clusters.

c$.$ considering only the two most similar observations in the two clusters.

d$.$ computing the average dissimilarity between every pair of observations between the two clusters.