Final answer:
Macbeth's tone in the first stanza of the song can be described as fearful. Therefore, the correct option is B.
Step-by-step explanation:
The word fearful best describes Macbeth's tone in the first stanza of the song. In this stanza, Macbeth expresses his fear and apprehension towards the upcoming battle. He uses words like 'fearful', 'forceful', and 'frightened' to convey his state of mind.