Multiple choice

Let G=(V, E) be a graph. Define $\xi(G) = \sum\limits_d i_d*d$, where $i_d$ is the number of vertices of degree $d$ in G. If S and T are two different trees with $\xi(S) = \xi(T)$, then

  1. $\mid$S$\mid$ = 2$\mid$T$\mid$
  2. $\mid$S$\mid$ = $\mid$T$\mid$ - 1
  3. $\mid$S$\mid$ = $\mid$T$\mid$
  4. $\mid$S$\mid$ = $\mid$T$\mid$ + 1
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 By the given condition, S and T are two different trees.  $\xi(S) = \xi(T)$ So, both S and T have the same number of vertices. Thus, |S| = |T|