Meter refers to the unit in poetry for rhythm and the beats pattern. Also known as foot, it has usually two or three syllables in each foot.
A word meter is derived from the Greek word 'measure'
With the lines of verse or poem, the meter also refers to the unstressed and a stressed syllabic pattern. Unstressed syllables are shorter and the stressed tend to be longer.
It has various types such as iambic meter, trochaic meter, spondaic meter.
Therefore, sentence which describes a poem's meter is D. Every three syllables in each line is accented