Which of the elements of poetry best contribute to the sound of the poem?

The rhythm, the rhyme, the meter and the cadence of the words used dictates the sound of the poem.

Explanation:

The rhythm of the words used depends on the stress of the syllables that are employed in the poem and give them their sound.

The cadence is similar and often relates to the theme of the poem in that a brooding poem will have harsher sounding words while a child's poem will roll off the tongue.

Rhyme is the use of similar sounding words at the end of the sentence.

Meter is the combination of number of stressed and unstressed syllables used in a poem in every line giving it its length and the structure.