For confusion on option D as answer.
The question starts from number of nodes = 3, because with 2 nodes there will be only one edge,
which violates the question condition.
For any cycle like figure the answer N seems legit because every time we can remove one edge,
and get one spanning tree, we keep doing this and finally we will have n spanning trees so m=n.
But there are counter case to it.
ABCDE is a graph with 5 vertices and 5 edges but we cannot achieve 5 spanning trees.
we can only go upto 4, so is 4 the answer no we can extend this logic to any no of nodes, but
this problem won't go away. But however for No of nodes >= 3 the value of m as 3 always satisfies.
Hence 3 is the ANSWER.