Explanation:

Correct Answer is (c).The given statement implies that holding simultaneous polls will have different effects on the national parties and the regional players. It is made clear by the fact that ‘but’ has been used to connect the two parts and it is used to connect two contrasting parts only.
Now coming to the Options, Option A is not correct since ramifications implies consequences and it seems right in the context but the second blank cannot be filled with conclusion since that will not make the sentence logical.
Option B is not correct because the word synthesis for the second blank is not correct. The first word impact for the first blank fits in the context
Option D is not correct because beginning cannot be used in the first blank as it will not make meaningful sentence. It makes the second word inconsequential to even consider for the second blank.
Option C will be the correct choice because the first blank can be filled with benefits whereas the second blank should have something that implies that there is an idea regarding the disadvantage of regional parties in case of simultaneous polls.
It makes option C the correct choice among the given options.