Multiple Choice

The set of full binary trees is defined as follows:

Basis: A single vertex with no edges is a full binary tree. The root is the only vertex in the tree.

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Recursive rule: If T$1$ and T$2$ are full binary trees, then a new tree T$\text{'}$ can be constructed by first placing T$1$ to the left of T$2,$ adding a new vertex v at the top and then adding an edge between v and the root of T$1$ and an edge between v and the root of T$2.$ The new vertex v is the root of T$\text{'}.$

Select the tree that is not a full binary tree.

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Group of answer choices

N$=$NULL $$

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$1$

$/\backslash$

$23$

$/\backslash$

$4$ N

N$=$NULL $$

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$1$

$/\backslash$

$23$

$/\backslash /\backslash$

$4567$

N$=$NULL $$

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$1$

$/\backslash$

$23$

$/\backslash /\backslash$

$456$N$$

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$1$

$/\backslash$

$23$