Answer:
A). Vigilant.
Step-by-step explanation:
Mood is described as the ambiance or atmosphere created by the author to elicit certain feelings or emotions of the author. Such atmosphere is created by the employment of words that proposes an emotional setting which aids to evoke desired response from them.
As per the given question, the words that best describes the mood of this poem would be 'vigilant' as it proposes a watchful and wary tone. The poet employs simile to compare himself to a deer who is always aware, watchful, and attentive. Thus, it offers a wary mood to the poem. Therefore, option A is the correct answer.