The correct answer is "the unstressed-stressed combination mimics waves". Iambic feet is a type of metrics used particularly in traditional English poetry to add an unstressed syllable followed by a stressed syllable. The name iamb comes from this combination of unstressed-stressed, while feet is the name given to a group of syllabes at which the rhythm is measured. In this case Whitman used iambic feet to accomplished the unstressed-stressed effect is his poem.