Humans, chimpanzees, gorillas, and orangutans are members of a clade called the great apes, which shared a common ancestor approximately 15 million years ago. Referring to the phylogenetic tree of primates provided below, answer questions 'a' to 'c'. (a) Which of the following pairs of apes are most closely related and why? (b) Which extant species is closely related to Homo sapiens? (c) Which extant species is the most distantly related to Homo sapiens?