Que. 
Let G be an undirected graph. Consider a depthfirst traversal of G, and let T be the resulting depthfirst search tree. Let u be a vertex in G and let v be the first new (unvisited) vertex visited after visiting u in the traversal. Which of the following statements is always true?

a. 
{u,v} must be an edge in G, and u is a descendant of v in T 
b. 
{u,v} must be an edge in G, and v is a descendant of u in T 
c. 
If {u,v} is not an edge in G then u is a leaf in T 
d. 
If {u,v} is not an edge in G then u and v must have the same parent in T 

Answer:If {u,v} is not an edge in G then u is a leaf in T 