jrk23 : To answer you please see below explanation.
A says only few are affected in last two weeks. Think about what the conclusion is in your own language. It says :
Ban should be implemented "in the last week" because polls "influence" people, "distort " their views.
Note the timeline. Ban on polls is not for all time. It is only saying
"in the last week". What about weeks before this last week? Think of it.
Now see what A says. It says, few people(1,2,3,... ) are influenced in last 2 weeks of polling. Translate in your language. Its simply saying that only 1,2,3, or "negligible" number of people are influenced in those last two weeks.
Imagine, I say people should stop eating pizza to reduce fat. But I say ban should
only be in the week prior to Christmas. Why?
Probably I am assuming that people eat pizza maximum in the week prior to Christmas?. So a potential weakener could weaken this assumption. Lets say,
Only 1 or 2 persons eat pizza in last week. If this is true, my conclusion is a dead chicken. Because it simply says that even if I do implement the ban, its not gonna have the expected result as only "few" people actually eat pizza in the last week. That's same as option A. I hope you see it.
Now for C, it strengthens because if polls do really eliminate motivation of voters to vote, isn't it the same as influencing them? The whole passage is stating that because polls "influence people", "distort views" (such as, do not vote), we should implement a ban. Our job is not to question the premise. The premise that polls influence people is not to be questioned. Accept it as true. But option C "reinforces" the strength of the conclusion by strengthening the premise a further level.