An undirected graph cannot be weighted

A directed graph contains no cycles

A directed graph always has a root

In a directed graph, edges have a direction (arcs); in an undirected graph, they do not

A set of keys and a set of values

A set of rows and a set of columns

A set of roots and a set of leaves

A set of vertices (or nodes) and a set of edges (or arcs)

A graph where all vertices are directly linked to each other

A graph with no cycles

A graph where every vertex has the same degree

A graph in which there exists a path between every pair of vertices

At the root of the tree

At the leftmost node of the tree

At the last leaf visited in pre-order traversal

At the rightmost node of the tree

No, because 15 should be to the right of 20

Yes

No, because 30 has no left child

No, because 35 should be the root

     20
    /  \
  10    30
 /  \
5   15

     20
    /  \
   5    30
    \
    10
      \
      15

     5
      \
      10
        \
        15
          \
          20
            \
            30

     10
    /  \
   5    20
       /  \
     15    30