option b and option d are false...
option b :
assume a cycle with three edges ( e1, e2, e3 ) with same weights.. Then one minimum spanning tree can choose e1 and another one can choose e2 and another minimum spanning tree can choose e3 etc ( by this example you can conclude option a is right ).
option d :
assume a cycle with three edges ( e1, e2, e3 ) with e1 and e2 with same weights and e3 with the weight less than e1.. Then minimum spanning tree choose always e3 and ignoring e1 and e2 always... Therefore only one minimum spanning tree exist.
option e :
minimum spanning tree's may be different but cost of minimum spanning tree always unique