DISCRETE MATHEMATICS GATE CS PYQ 2010

Let G = (V,E) be a graph. Define ξ(G) = Σd id x d, where id is the number of vertices of degree d in G. If S and T are two different trees with ξ(S) = ξ(T),then
|S| = 2|T|
|S| = |T|-1
|S| = |T|
|S| = |T|+1