i found this ex

Let G = (V;E) be a graph. Show that the follwing two problems are NP-hard. 1. G has a spanning tree where every node has at most k neighbors and k is part of the input. 2. G has a spanning tree where every node has at most 5 neighbors.

It's wrote than 1 is supposed to be a hint. You can of course choose to ignore it and solve 2 directly.

I tried to reduce K-MST to Steiner tree, but i don't know if is a right way. I read that can use an Hamiltonian circuit, but i don't understand how to do. Someone can help me?