Walt Whitman was a pioneering figure of American poetry. His innovation first all lies in his use of（）， poetry without a fixed beat or regular rhyme scheme.

Walt Whitman was a pioneering figure of American poetry. His innovation first all lies in his use of（）， poetry without a fixed beat or regular rhyme scheme.
A、blank verse
B、heroic couplet
C、free verse
D、iambic pentameter
正确答案：C