Final answer:
The line from 'The Silken Tent' that features both alliteration and assonance is 'At midday when the sunny summer breeze,' which utilizes the repeated 's' sounds and the 'u' vowel sounds.
Step-by-step explanation:
The line from Robert Frost's poem "The Silken Tent" that uses both alliteration and assonance is:
A. At midday when the sunny summer breeze
Alliteration is the repetition of the same consonant sounds at the beginning of closely connected words, which in this case can be seen in the repeated 's' sound in "sunny summer." Assonance is the repetition of vowel sounds within close proximity, and this line exhibits assonance in the repetition of the 'u' sound in "sunny" and "summer." This poetic device combination enhances the rhythm and musicality of the verse.