The correct answer is B. Blank verse is a form of verse that uses iambic pentameter.
As the name itself says, a blank verse is a type of verse, stanza, part of a poem, they way a poem is written. Blank verse means that no rhymes are used throughout the poem.
Usually, blank verse uses iambic pentameter - this means that each word consists of two syllables (where the first one is unstressed, and the second one is stressed), and that there are 10 syllables within one line (meter consists of 2 syllables, and penta means 5). Shakespeare wrote his plays using blank verse.