How was the starting vertex chosen in this solution?

Question

From Rosen's Discrete Mathematics and Its Applications, 3ed, chapter 11 p. 799-800:

The solution given only shows a graph starting from vertex b. I wonder if this is arbitrarily chosen, because there are 3 edges of weight 1 and 6 vertices to pick from.

Answer 1

Prim's algorithm produces a correct minimum spanning tree regardless of which vertex it starts from. The choice of $b$ was entirely arbitrary.