Poems that do not follow specific rules are called:

A: iambic verse

B: fixed verse

C: free verse

D: syllable verse

The correct answer is free verse (choice C), in which you do not follow any particular rules about rhythm or rhyme. On the other hand, iambic, fixed, and syllable verses follow a certain rhythm, to make the poem look more uniform. Free verse is not restricted in such a way, and allows author to write as the wish.