In any reaction more acidic product will not form if more acidic product will form then reaction can't go in forward direction. in d part water is form which is more acidic than alkyne so d will not the ans . in A and c part also more acidic product water is form so not possible. hope this helps.
Thats ok but sulphur have vacant d orbital which stabilize this negative charge i.e electron its like just giving a house to electron to stay