The main purpose of a persuasive speech is to
a. make readers think and present them with options.
b. convince readers that your viewpoint is correct.
c. convert readers to the idea that no one can really know the truth.
d. shame readers by showing them that what they have believed is wrong.

In order to persuade, one must not put down another's ideas or shame them. If they do, usually it's not the main purpose of the speech. (D) is incorrect. When someone persuades, they always try to get the reader to believe their story. For example, if Donald Trump or Hillary Clinton is holding a rally, chances are they're not going to say, "Oh, you can vote for my opponent". Instead, they'll try to slander their opponent and say how voting for them would cause the country to be destroyed. This immediately rules out (C) and (A). Therefore, the answer is (B).

Where is the rest of the question?