The correct answer is: Free Verse.
Walt Whitman's "Leaves of Grass" is a collection of poems that was first published in 1855. Since then Whitman rewrote and added material. In over four decades of work, Whitman produced many well-known poems such as 'Song of Myself' or 'I Sing the Body Electric'. With the exception of one particular composition, all poems in this collection were written in free verse, whithout following the traditional standards for meter and rhyme. In that sense, Whitman's greatest legacy is the renovation of form. It's important to recognize that, despite the freedom of verses, many lines in Whitman's production approach iambic meter, which is a very classical form. That is because the iambic meter produces a very natural sound, like in conversation, as Whitman intended because of his democratic and philosophical view.
