The answer is letter A. It is the mood created by words in the poem.
Tone in poetry is the attitude of the poet towards the poem's reader, subject matter, or speaker as it is interpreted by the reader. It is usually described as the " mood" which pervades the experience of reading the poem. This is created by the vocabulary of the poem, metrical regularity or irregularity, use of figurative language, syntax and rhyme.
The tone of the poem is the attitude which is implied by the poem's style.