It's B.
Analysis of Argument :- illegal immigration is an important issue. One candidate plans to deport illegal immigrants whereas other does not. 60% of residents opposed the plan whereas 35% supported it. So the conclusion is, the candidate who oppose the plan will win the election because he enjoys support of 60% residents. There are several things which must have assumed while drawing the conclusion and if did not they will weaken the conclusion. Any choice that contain reasoning reverse of them will be incorrect here 1) all or substantial residents do posses the voting right. 2) all or substantial residents that oppose the plan would actually vote on election day. 3) all or substantial residents that oppose the plan would cast their votes to the candidate who also oppose this plan.
A) Incorrect. This clearly weakens the argument by saying voters do not vote on the basis of candidates' position on illegal migration
B) This choice stays neutral and is correct answer.C) Incorrect. If substatial voters who oppose the plan have no voting rights then it is difficult for that candidate to win. Weakens the argument.
D) Incorrect. This says there are other factors than illegal immigration on which voters decides whom to vote. Otherwise the candidate who supports the plan would have not been elected again and again
E) This choice seems not to weakens the argument at first(so i kept it as a contender initially) but if look closely it reveals that the residents are devided in three sections 60%(opposers), 35%(supporters), and 5%(neutral). Now the percentage of illegal immigrants is possibily 28% or 29% (just under 30%)and those should must be in 60% section. if those 28% have no voting rights then the candidate who oppose the plan would left with only 32% supporters who can actually vote and can not win the election with that. This weakens the argument. Incorrect.