Exercise 1.

Which of the following graphs are trees?

1. \(G = (V, E)\) with \(V = \{a, b, c, d, e\}\) and \(E = \{\{a, b\}, \{a,e\}, \{b, c\}, \{c,d\}, \{d,e\} \}\)

2. \(G = (V, E)\) with \(V = \{a, b, c, d, e\}\) and \(E = \{\{a, b\}, \{b, c\}, \{c,d\}, \{d,e\}\}\)

3. \(G = (V, E)\) with \(V = \{a, b, c, d, e\}\) and \(E = \{\{a, b\}, \{a, c\}, \{a,d\}, \{a,e\}\}\)

4. \(G = (V, E)\) with \(V = \{a, b, c, d, e\}\) and \(E = \{\{a, b\}, \{a, c\}, \{d,e\}\}\)