https://stackoverflow.com/questions/1787152/prims-mst-does-the-start-node-matter this show that you can start from any vertex
https://www.cse.ust.hk/~dekai/271/notes/L07/L07.pdf
refer to page 16
they are saying take any vertex and take the minimum edge to that vertices set that dont make cycle repeat this step until you got all vertices
in option A (c,d),(d,f) now taking (a,b) edge is wrong
in option B they started from the vertex e and grow and each step they took the minimum edge and at the time when choosing the third edge they can choose either of (b,f) and (c,d) they choose (b,f) and move ahead so this is right
in option C they started from the vertex e and grow and each step they take the minimum edge and at the time when choosing the third edge they can choose either of (b,f) and (c,d) they choose (c,d) and move ahead this is right
in option D (d,f) now taking(d,e ) is wrong
