(a) Give an example of a graph in which every node is pivotal for at least one pair of nodes. Explain your answer.
(b) Give an example of a graph in which every node is pivotal for at least two different pairs of nodes. Explain your answer.
(c) Give an example of a graph having at least four nodes in which there is a single node X that is pivotal for every pair of nodes (not counting pairs that include X). Explain your answer.