Which of the following statements about hierarchical clustering is true?

a. Because of its nested design, hierarchical clustering will find the set of k clusters that maximizes the average silhouette meaure for all possible values of k.

b. For the same number of clusters and same distance measure, the clusters resulting from a k-means approach and a hierarchical approach will be the same.

c. Hierarchical clustering is not affected by outliers.

d. A dendrogram shows how to group observations into varying numbers of clusters.