Our sweetest songs are those that tell of saddest thought.

"a" because he is appealing to logic as oppose to appealing to the audience's emotions.

from the political point of view it could be said that the candidate   is an effective speaker because she takes a strong position on the issue. it is an open discussion but probably she is making a presentation and can choose which subjects she wants to address. she is very likely to attain her aim which is to convince voters to accept her proposal.