Which form does brutus’ speech use?
a.) blank verse
b.) prose
c.) sonnet
d.) rhymed iambic pentameter

The form the Brutus' uses in his speech is in letter B. Prose. Prose is a form of language that has no formal metrical structure. It applies a natural flow of speech, and ordinary grammatical structure rather than rhythmic structure, such as in the case of traditional poetry. I hope this would help

I believe the answer is: B. Prose

Prose refers to the language that is used without any Grammatical structure.The flow of speech in prose is usually has natural flow and often used in day to day conversation.
Here is an example of Brutus' prose: 
Romans, countrymen, and lovers! Hear me for my cause,