Explanation : If no two edges of G have same weight surely G will have unique spanning tree is true.
So I is true
Also if, for every cut of G, there is a unique minimum weight edge crossing the cut then G will have unique spanning tree is also true. So II is true
[Note: The converse of II is not true, but that is not relevant to this question]
So both I and II are true.
Option (C) is correct.