OPTION a is correct
--> if all weights are distinct values then there exist unique min/max spanning tree.(option a)
Knowing the other option is also important while preparation ::
--> if graph is cyclic graph(n vertices) with same edge weights then there exist n spanning trees.(option b/c)
--> //y if graph is complete graph(n vertices) with same edge weights then there exist nn-2 spaning trees (option e).
//up vote if you agree.