In stanza 5 of the poem, the line "And in the hush we joined to make" suggests a quiet and attentive atmosphere as the characters are listening intently for the sound of the brook. The use of the word "hush" functions as onomatopoeia, creating a sound effect that emphasizes the silence surrounding the characters before they dare to look. This contributes to a mysterious tone because the hush creates an air of suspense and anticipation, making the moment feel more significant and enchanted. Therefore, the correct response is:
A mysterious tone is developed through onomatopoeia in the word “hush.”