Answer: A. a poetic foot made up of an unstressed syllable followed by a stressed syllable.
Explanation: In poetry, an iamb is a foot or beat consisting of an unstressed syllable followed by a stressed syllable, or a short syllable followed by a long syllable, iambic foots were used in traditional traditional English poetry and verse drama. So, according to this information, the correct answer is the definition given by option A: a poetic foot made up of an unstressed syllable followed by a stressed syllable.