The answer is A. A pattern of stressed and unstressed syllables
Step-by-step explanation:
In poetry, the meter refers to the structure that determines the rhythm, this is based on the number of syllables the poet includes in each line and the combination of stressed and unstressed syllables that create a specific pattern. For example, in English poetry one of the most common meters is the pentameter iamb that includes ten syllables in each verse and a stressed-unstressed syllable pattern but besides pentameter iamb, there are many other patterns. According to this, the meter can be defined as "a pattern of stressed and unstressed syllables".