Hey!! The answer is, A. Amy, Megan! A predicate nominative is the noun following a linking verb that restates or stands for the subject!
I'd say the answer is D.
The definition of the word discern is "1.Perceive or recognize something. ex; I can discern no difference between the two policies."
2. "Distinguish (someone or something) with difficulty by sight or with the other senses. ex; She could faintly discern the shape of a skull."
Thoreau mostly uses imagery to illustrate time in the excerpt. The second sentence is saying that he is in the midst of time/living, and he can "detect how shallow it is," meaning that he is aware that life is short and that the end is inevitable. Thoreau also describes time as being fleeting, but ever-present.
I hope this helps!
