25. If an edge is added from the vertex with subscript 3 to the vertex with subscript 6 in each graph in Exercise 23, which of the resulting graphs will have Hamiltonian circuits and which will have Euler circuits?
25.
(a) Hamiltonian circuit: yes; Euler circuit: no
(b) Hamiltonian circuit: yes; Euler circuit: no
(c) Hamiltonian circuit: yes; Euler circuit: no
(d) Hamiltonian circuit: no; Euler circuit: no